I have read he was the vice presidential nominee to McGovern for only 2 weeks after chaos at the convention briefly put him there. And of course McGovern lost.
As evidence that the Democrats would not pay a heavy price in lack of unity if Sanders somehow being snubbed by some power move, this example seems completely lacking.
The point is, if Hillary is out, at any point up until about 45 days before the election, Biden/Warren could be in.