I mean, in the event of a brokered convention, it also falls on the party leadership not to self-destruct. Sanders voters will not show up to vote if he has a sizable plurality but is not given the nomination. He has high favorables among the party electorate and a lot of grassroots enthusiasm behind him - nominating him will not depress the moderate turnout in any way.
Your post is doing a lot of hypotheticals here, especially the last sentence. No matter how popular Bernie may be with Moderate Democrats (who are NOT moderates, no matter how much people want to pretend they are) you still need a hell of a lot more people than your base to win an election. If Bernie is toxic among our new coalition that has, in part, college educated suburban voters, he totally 100% can lose and depress turnout. One cannot argue that Bernie's demographic weaknesses don't matter, but Biden's do.
As to your first point, not self-destructing does not entail "Bernie gets everything he wants, and everyone else can fuck off." It doesn't involve telling the 30-50% of the Dem electorate who didn't vote for Bernie "get in line or else." That's not how this works. There absolutely has to be give and take from both sides. That means Bernie doesn't get everything he wants and THE ESTABLISHMENT doesn't get everything they want.
Honestly, if we get close to a brokered convention, all of this will be settled behind the scenes. An ideal scenario would be let the first round vote, Bernie has a plurality or whatever....then before the second round happens, whoever is in 2nd comes out and asks to suspend the rules and vote for the nominee by acclimation.
Edit: On the first ballot, delegates are bound to their nominee. On the second ballot, everyone becomes unbound and they can vote for whomever. If your nominee tells you to vote for Mickey Mouse, you can if you want to, but you do not have to. There's no mechanism to force a delegate to vote for the person their nominee asks them to.