It looks like Klobuchar will beat Harris out for fifth in both IA and NH. That kills Harris unless she wins in SC (she is currently polling 5% there) and gives us the top four. And then those four run for a while. Biden never gets out no matter what, it's his last dance. The loser of the Sanders/Warren h2h eventually drops out and endorses the other. Let's say that's Warren for the sake of argument.
The question is, what shape is the Democratic electorate in the primaries? If it's anything north of 60/40 Centrist then Biden probably wins the nomination unless he completely collapses. With say a Biden/Pete 70/30 split and a Center/Left split of 60/40, Biden comes into the convention with 42% of the electorate which translates to over 50% of the delegates.
Likewise, a Center/Left split of 50/50 means the combined delegates for Warren and Sanders are going to be around 50% and the leader between them will also lead the field. Since delegates remain committed on the first ballot that means Warren (remember, we're assuming she's the Left survivor, but it could as easily be the other way) is in the low 40s on the first ballot. The second ballot happens and the superdelegates are released. If Biden is trailing Warren significantly (>5%) then, with the Sanders delegates moving to Warren, the superdelegates will make it a love in and indeed at that point I would expect a nomination for Warren by acclamation to start the hugs and kisses.
If Biden completely disintegrates, as in the final Center split is like 70/30 Buttigieg, then the Biden delegates and supers push him through on the second ballot regardless of the Center/Left party balance, because the supers have an excuse to hose the Left (again).
So, there are ways for each of four to win. At this point the odds I'd lay are:
.1 a convention white knight. Let's say Sherrod Brown to swing OH and the election.