Yeah, at this point basically one person has the vast majority of pledged delegates but changed their mind about running, so you now have (nearly) all unpledged delegates, plus I guess there's still super-delegates too. Nothing technically happens until the roll call at the convention. Though even if Biden had stayed in, nothing technically would have happened until the roll call at the convention either. The main difference being, the delegates would still be pledged then to vote for Biden, with whatever level of bindingness that ever had, damned if I know. The candidate can release pledged delegates at any time as far as I'm aware; we've seen second place finishers like Hillary in 2008 release their during the roll call to give a sense of unanimity. Of course, the person in first releasing theirs is a new thing. So until the convention I guess they're technically unpledged and can do whatever they want; they could all change their minds at the convention I suppose; but I think the delegates all realize time's-a-wastin' and it's good to get behind a single person sooner rather than later. And if anyone was for all intents and purposes on the primary ballot with Biden when people voted in their primaries this spring, it was Harris, so she is by far the most logical, reasonable, and fairest person to endorse and gather behind. But again, nothing as far as I am aware is in stone until the actual convention.