If the risk is that someone like Romney, or McCain get in, I think progressives would feel more free to take risks and pick a more progressive candidate. To most progressives, while they're not fans of Romney and revisionism aside weren't fans of McCain, having one of them in power feels less dangerous than having Trump in power.
If next election they're up against an attempt for Trump to get back in, then yes, you could expect a large progressive turnout for a Biden re-election. But if he's against a more moderate republican, I don't think you'll see the turnout that happened this year repeat, which may turn out to be a problem for his supporters.