The problem is that there really isn't any way at this point for Democrats to replace him as the candidate involuntarily. Most of the ballot deadlines are passed, and he's the only one on many of them. So it has to come from him/Jill.
I think last night's train wreck actually makes that less likely. He's been accused very publicly of mental incompetence, and is angry about it. Can't see him backing down at this point because that would amount to a concession that the Special Counsel's assessment was correct. There's no chance of any other, more innocent explanation that "I just want to enjoy my retirement/want to give someone else a chance," etc.. incompetence would be the unavoidable explanation, and he's not willing to admit that. Nor is his wife.