If I may be permitted to state the obvious, Bernie was clearly right to reject this priceless advice https://www.lawyersgunsmoneyblog.com/2020/04/could-bernie-have-won-by-ramping-up-attacks-on-biden-spoiler-no

What doomed Bernie’s campaign was his failure to win voters who had positive feelings about him but also have positive feelings about the Democratic Party. Could you convert these voters by going nuclear on Obama’s well-liked vice president? The question answers itself.

And -- to make this relevant to today's events -- by preserving his relationship with Biden rather than doing a scorched-earth campaign with a 0% chance of succeeded, he's kept up a good relationship that will allow him to influence a Biden administration, which is important!