Neither of the parties have had their conventions yet and officially nominated anyone so it could still be anyone from any side. If Joe drops out before the DNC then the delegates that he won during the primaries are free to vote for whoever they want.
I was reading about it and the DNC has to do some fuckery at the convention because it hasn't happened in a long time if ever, but that's no big deal. They got rid of the super delegate thing which makes it harder to get consensus on one candidate. There are a couple of states that they'd have to change the laws because it's too late due to ballot printing laws, I think Michigan was one, so you know that starts lawsuits for the sake of lawsuits. None of his fundraising can go to another candidate, but I'm sure there's an unknown loophole or they just do it and pay the minimal fine for it.
I think he stays in regardless.