The rumour mill is claiming that if Hillary drops out they will replace her with Uncle Joe:

DNC delegate: If @HillaryClinton withdraws, every indication now committee will vote to replace with Biden. @BernieSanders team scrambling

Look, the Dems have essentially three choices:

1. Keep running Hillary. As Scott Adams so eloquently points out, she will lose because she showed unacceptable weakness at an American "holy place". I had come to about the same conclusion because of the mythical weakness of illness, but the argument is similar. People need to get over the idea that elections are rational - they are not. Mythical and irrational elements are just as important.
2. Uncle Joe or some other DNC bigwig (including Kaine). The sound of millions of Bernie backers screaming out in anger at being screwed again will doom the sacrificial lamb. They will stay home.
3. Bernie. All of a sudden, you have someone with positive approval ratings who can actually win.

The choice seems pretty obvious, but that hasn't stopped them before.