Fruits
Leonel really wanted to punch his grandfather in the face, but he felt that that might not be appropriate given the moment.
He had really been about to let the old man go. When you were faced with these sorts of issues, the only person who could choose to live was the person themselves.
Unless Gervaise could realize that being an Emperor was never something he wanted, but something he had forced, hypnotizing himself into believing he wanted, then there would be no amount of bringing him back that would change anything.
In the end, if he had revived his grandfather without his input into it, then they would have just ended up locked in battle again and Leonel would have been forced to kill him once more.
Or… Gervaise might have accepted his loss and become a twisted version of the man Leonel knew him to be.