I think his health collapse is scheduled for the week of the Democrat Convention. If Bernie lacks plurality of votes, it all goes wide open and Michelle or Hillary can be selected.
But I think Joe’s health collapse is already penciled in on someone’s calendar.
I think that Joe Biden is the ultimate stalking horse but I don't think he knows it. When he has effectively eliminated Bernie and the timing is right, the DNC will inform Biden that he is stepping down as the candidate due to his diminishing mental capacity. If this is after the convention, watch who the DNC forces Biden to take as VP. That is the person who the powers in the party want. (Personally, I don't think it is Hillary but instead someone to lead the next generation of Democrats).
I don't see Biden doing his Thomas Eagleton disappearing act before the convention. Too messy with Bernie being able to claim the right to the nomination and also it would throw it open for anyone to toss their hat into the nomination process and the DNC could lose control of the process. I think the DNC wants Biden to get the nomination and then quietly step aside for the VP who the DNC got to hand pick.