There's no use overthinking about it because overthinking about it won't do him any good. He just has to make a decision and stick with it. If he could see the future then he might be sure of his decisions and their repercussions but he can't. He can read the past, unfortunately for him, this world doesn't have a past. It was created instantaneously. It doesn't have a history for him to base his decisions on.
If someone unrelated to Legion can volunteer to help Legion and even go so far as to sacrifice her consciousness, then he can surely offer himself to die for Legion. If his decision turns out to be bad, then he will pay the price for it despite knowing how bad the price might be. It is a risk that is worth it.
