CNN says that talks to create the Democratic party’s Dream Team are underway. The word "difficult" was used, as you’d expect, given that Hillary has a very good chance of winning the aggregate popular vote.
Partisan voters almost always come home after their candidate loses. The problem arises when a candidate’s supporters believe that their guy (or gal) didn’t lose.
I don’t think that will true in the Obama-Clinton case, however. Unless Hillary has been saving a last wad of oppo to shoot across Obama’s bow as she’s going down in defeat, her supporters will go over to his camp in large numbers.