This was decided last October. You know, Biden met with Warren at his residence, and then scheduled that Rose Garden press conference where he was supposed to announce. Seemingly at the last second, he switched from "yes" to "no", but neither he, nor Warren, nor Obama have endorsed Hillary.
That's because Obama and Biden, and perhaps Warren as well, know the day and the time Hillary, Bill, and Chelsea are going to be arrested for money laundering, tax evasion, racketeering, fraud, bribery, espionage, and conspiracy.
But it's important that Bernie be shut out, conclusively, of a majority of delegates first. If that's not done then, yes, his supporters will be correct that they have been robbed.
But Bernie is not entitled to a single Hillary delegate, and he's not entitled to a single superdelegate.
So, I imagine the bust will go down 7-10 days before the convention, so the media can ramp up the hysteria about the "crisis" (they'll even call it a "constitutional crisis", even though the parties and "running for President" aren't IN the Constitution).
When the convention assembles, the delegates and the media will not know what's going to happen.
And when Joe and Elizabeth walk out on that stage, the hall will go crazy. Obama will make the nomination speech ("Our long national nightmare is over"), and that will be that.
You’re assuming that Hillary will “go quietly”. I would not make any such assumption. In fact I’d be more inclined to believe that the reason Biden declined to run and has repeatedly said he’s not interested since then is because Hillary has the dirt on Obama and a whole lot of others and has made it clear that if she goes down she’ll take the lot of them down with her.