At that time, Liu Bei was obedient to Zhuge Liang. How could Liu Bei let Zhuge Liang go to the front to kill the enemy? This had to be done by Liu Bei himself, and Zhuge Liang waited for Liu Bei to come back. However, this situation in the battle of Yiling was not the result that Zhuge Liang could have thought of, which led to a mistake in his plan at the beginning. Therefore, the problem will gradually emerge when fighting, and Liu Bei will eventually fail.
Even if Zhuge Liang goes, it won't help, because even if he can change his plan in such a short time, the chances of success are slim. So whether Zhuge Liang goes or not, the final result is Liu Bei's defeat. In addition, Liu Bei felt that he was sure of winning, and he didn't mean to take Zhuge Liang with him, so Liu Bei's carelessness led to his failure.
To sum up, Liu Bei's failure has little to do with Zhuge Liang, because a person has played a small role in a war, so Liu Bei will not win with Zhuge Liang.