If after Zhuge Liang's death, Wei Yan took over Zhuge Liang's command to continue the Northern Expedition, I think it would be difficult for him to defeat the State of Wei. However, the situation in Shu Han was much better than when Jiang Wei was in it.
Wei Yan was the first general in the middle and late Shu Han Dynasty. His military ability was the strongest in the Shu Han at that time. After Zhuge Liang's Northern Expedition, he had been using Yang Yi's most Zhuge Liang's left and right hands. Wei Yan's official position and title were second only to Zhuge Liang in the Shu Han Dynasty. In terms of military affairs, Zhuge Liang could not do without Wei Yan for a moment. Because of his dependence on Wei Yan, Zhuge Liang never wanted him to leave his control. In many Northern Expeditions, Wei Yan has been serving as the front of Zhuge Liang, fighting bloodily.
However, Wei Yan was appointed as the Taishou of Hanzhong during the time of Liu Bei, and was a major officer in defending the northern gate for Shu Han. In Liu Bei's Northern Expedition arrangement, Wei Yan was not only a local official, he was the vanguard of Liu Bei's Northern Expeditionary Army that spent qin chuan. Behind him, zhang fei and Ma Chao's soldiers and horses were also arranged as backups. Once the Northern Expedition began, Wei Yan would be the first general to send troops.
Unfortunately, later because of the defeat of the Eastern Wu Alliance, "Longzhong Pair" went bankrupt. Liu Bei changed the direction of his troops, successively transferred his troops to the east, and launched the Battle of Yiling. This made Wei Yan's task defensive.
However, Liu Bei must have discussed the strategy of the Northern Expedition with Wei Yan before his death. The so-called "Meridian Valley Conspiracy" should be the result of Liu Bei and Wei Yan's peace talks. However, by the time of Zhuge Liang's Northern Expedition, the gap between Zhuge Liang and Liu Bei's military ability was too great, and their personalities were different, and he finally did not adopt Wei Yan's suggestion, which dashed Wei Yan's hopes.
Moreover, in order to prevent Wei Yan from acting independently and undermining his own strategy, Zhuge Liang rarely let Wei Yan act independently. The only time Wei Yan acted independently was when Wei Yan and Wu Yi entered Qiangzhong in the west together. Wei Yan led a light horse, carrying a large amount of Shu Jin's treasures, attacked the west from the east, mobilized Cao Wei's Guo Huai troops, and took advantage of the void to enter Qiangzhong. In a short period of time, Wei Yan built up a cavalry of tens of thousands. Then, in the Battle of Yangxi, he defeated the famous Cao Wei general Guo Huai, successfully returned to the army, and won a rare victory against Cao Wei.
Wei Yan possessed superior military ability, but was at odds with Zhuge Liang's strategic and tactical thinking. In addition, Zhuge Liang's use of him was not in line with his wishes, so he always complained about Zhuge Liang's timidity, saying that his talents could not be fully exerted.
When Zhuge Liang died, Wei Yan thought that the opportunity he had waited for for many years had arrived. When Fei Yi came to test his attitude, Wei Yan directly stated that he would take over Zhuge Liang's command and continue the Northern Expedition. Unfortunately, his political ability is too poor. In the end, he was killed by Yang Yi and the entire clan was wiped out.
We can infer the following inferences from the situation of shu Han in the period from the time of Zhuge Liang's death to the time of Wei Yan's death. Some of the things that would happen after Wei Yan could successfully take over Zhuge Liang's power.
First, Wei Yan would not withdraw his troops, and he would continue to fight with Sima Yi.
We can see from wei Yan's conversation with Fei Yi that Wei Yan was not in favor of withdrawing troops. What he meant was to have the civilian officials around him escort Zhuge Liang's coffin back to Sichuan and continue to command the army's Northern Expedition.
Then Wei Yan took over the army and would replace the personnel and army deployment. In this regard, Wei Yan also expressed his opinion to Fei Yi. Unfortunately, Fei Yi had already accepted Zhuge Liang's secret plan and no longer obeyed Wei Yan. Therefore, he verbally promised Wei Yan, but found an excuse to run away and betrayed Wei Yan.
We can see from the retreat of the main force of the Shu Han army that first, Yang Yi and others were too poor in military ability and were extremely afraid of Wei Yan, so they retreated in a hurry. So much so that even grain and top-secret military books were discarded. Second, the generals that Wei Yan replaced were definitely most of Zhuge Liang's generals, which would cause public anger, and everyone abandoned him together. In the middle of this, Fei Yi played a great role.
Second, Wei Yan would take positive action against Sima Yi.
We have seen that after Wei Yan took over the army, he first had to change the general of the army. This meant that Wei Yan would take a completely different military action from Zhuge Liang.
There were not no talents and generals in the Shu army, but they were all abandoned by Zhuge Liang because they were not in line with their wishes. And Wei Yan knew the generals of the army very well, and who could use them was clear. For future military operations, Wei Yan would promote and appoint those real generals. In this way, the combat effectiveness of the Shu army will be greatly improved.
Wei Yan had been stationed at the forefront during the confrontation with Sima Yi. According to the history books, his large camp was prominently placed ten miles before the main force of the Shu Han Dynasty. He could be said to be very familiar with Sima Yi's deployment, and in his mind, he already had a plan on how to defeat Cao Wei's army. As soon as he took over the army, he would put the plan into practice.
Third, Wei Yan would give Cao Wei a big blow in a short period of time and have an advantage.
After Wei Yan took over the army, he would follow his plan. Wei Yan's military ability was far stronger than Guo Huai's, and Guo Huai's level was slightly better than Sima Yi's. Therefore, in a short period of time, Wei Yan would seize the loophole he found sima Yi and deal a heavy blow.
Wei Yan could use qi with his troops. Sima Yi did not know that Zhuge Liang was dead, too late to change the defensive deployment, coupled with the long-term confrontation, the slackness of the army, which would cause Wei Yan to be defeated in one fell swoop and suffer huge losses.
However, judging from Sima Yi's use of troops, Sima Yi was also very cautious in his use of troops. Although his defense was mainly based on Zhuge Liang, he had a contemptuous heart for Zhuge Liang. However, he will not leave too many loopholes.
We can see in the history books that Sima Yi's camp layout was a continuous defense system. Even if Wei Yan broke through the front line, the rear defense line could still continue to defend.
Therefore, according to my judgment, the most likely method for Wei Yan to take is to surprise the soldiers interspersed with the envelope and cooperate with the frontal army to attack the Wei army. He attempted to tear a gap in the Cao Wei defense system that surrounded the Defending Shu Army in a semicircle, dividing and encircling the Cao Wei Army and breaking it each other.
But this military operation is very difficult. The Shu army trained by Zhuge Liang could not achieve this. Therefore, although Wei Yan was able to strike at Sima Yi with a surprise attack at the beginning, it was difficult to break Sima Yi's defense line in the end, and he could only be forced to withdraw.
Fourth, Jiang Wei's qualifications were too shallow at that time, but he could become Wei Yan's right-hand man.
After Wei Yan withdrew, he would face a very complicated political situation. Wei Yan was only a military general and lacked political acumen. Politically, Zhuge Liang's Chancellor's Mansion still occupied a dominant position. They still suppressed Liu Chan and exercised Zhuge Liang's power.
Wei Yan, on the other hand, was loyal to Liu Shi, and he would agree with Liu Chan to form a political united front. In this way, the Shu Han dynasty will produce a new pattern.
Jiang Wei's qualifications were too shallow, and after Wei Yan's death, he was preceded by Wu Yi, Wang Ping, Jiang Huan, and Fei Yi. Therefore, he couldn't help Wei Yan much at all. However, both Wei Yan and Jiang Wei were loyal to Liu Chan, and under Liu Chan's command, they would reach a military consensus and jointly carry out the Northern Expedition.
Jiang Wei's military ability was not as good as Wei Yan's, but he preferred to use danger and strangeness than Wei Yan. In this way, Jiang Wei would be Wei Yan's right-hand man. Wei Yan's multi-year plan will be smoothly implemented. In this way, Cao Wei's side will never have a peaceful day.
epilogue:
If Wei Yan had not died of infighting, he would have taken over the military power of the Shu army. With his support, Liu Chan would take back the monarchy that should have belonged to him. In this way, the political situation of the Shu Han Dynasty will change. With the support of Liu Chan, Wei Yan would become the main general of Wei.
Wei Yan would select and appoint talents according to his vision, and the Shu army would soon get rid of the decay and decadence of the past. The Shu army will have a new look and double its combat effectiveness. With the help of Jiang Wei and a number of other newly raised generals, Wei Yan would bring great trouble to Cao Wei. Under his command, it would deal a great blow to Cao Wei, and it was likely to take Guanzhong and confront Cao Wei at Tongguan, laying a better foundation for the future Shu Han regime.