Somewhere down the line, I’m sure Hannibal is going to get the morbid idea that the best way to ensure that Will always remembers him is to make sure he dies in front of his eyes. Even better if he’s the one to kill him and he personally sees the light go out of his eyes.
If anyone knows Doctor Who, you know what I’m talking about. When the 10th Doctor watched The Master dying in front of his eyes, he begged him to regenerate, but he spited him and didn’t. He knew it would haunt him if he died. The last two Time Lords in the universe (at the time) and he purposely left The Doctor alone as he made him watch him die. And this spiteful stunt haunted him for a very very long time.
Hannibal has a weird gap in his knowledge and mind where he believes that Will will never love him the way he loves him. He won’t ever want a life with him, because he will always reject it no matter how much he may chase it. And since he threatened to forget him once, he’ll eventually do it again. Not untrue. So long as they’re both alive, this can always still be true. But if one of them died, this would no longer be true. Hannibal doesn’t yet know the full impact and influence he has on Will, because he assumes Will is capable of moving on without him. Or at least he can try to by manipulating the people around him. So naturally and eventually, his mind may take him to a very dark and creative place where he thinks that if Will won’t remember him in life, he might as well remember him in death. Just as Mischa did to him upon her death or so he can hope.
Granted, Will is capable of erasing things in history if it’s inconvenient to him. He did that with Abigail and he was already on his way with doing it with Molly and Wally once they no longer fit his idealistic needs. By theory and past patterns, he could do that with Hannibal. If that’s the case, then Hannibal is going to probably orchestrate his own death in a way that’s so unbelievably horrific and traumatic that Will couldn’t possibly ever forget him.
When it comes to Will, Hannibal can get very desperate and self destructive. The ways in which he would do things to spite and haunt Will forever are endless, but there’s probably a lot of ways in which he can attempt to do this. It doesn’t necessarily mean he’s suicidal. It means he’s willing to completely destroy himself in order for Will to remember him for as long as he lives. And since he himself is dead, he would no longer have to worry about it anymore.