Biden, Sanders, and Warren will be in this until the end unless one of their campaigns crashes spectacularly. Buttigieg I still don't see as having much of a chance, so there will come a time where that becomes too painfully obvious and he has to drop out. Harris will be out after California when she doesn't even make the top 3, possibly doesn't get any delegates at all. Bloomberg and Steyer will do it until they get bored, because they have nothing better to do and essentially infinite funding so no other incentives to stop. Deval Patrick I'm not sure, because he seems to have an absolute nothing campaign as it stands and jumping into the race at this point was pretty delusional on his part. Gabbard has nothing better to do so she'll continue until she runs out of money. Yang is one candidate whose campaign has not yet peaked, so it's hard to say how far he'll go, he could be out before Super Tuesday, or he might last longer and have a similar fate to Buttigieg. Everyone else is irrelevant and will drop out either before or immediately after Iowa. Booker and Klobochar will probably be after-Iowa dropouts, unless they really start to struggle financially. Bennet might be before Iowa. Delaney and Williamson and Castro could all go either way, depending on what suits their ego. Really that could be said of any of the remaining candidates. Sestak and Bullock dropped out now because they're less embarrassed at the idea of dropping out before Iowa than they are of the idea of getting 0% in Iowa.
Sestak, why the hell did you even waste your time? I'd say you wasted everyone's time, but no one noticed you were there so you really only wasted your own.