I’m not sure what you see, that I’m missing. However, what I see, is that if Biden refuses to go along with progressives, they will blow up the party. That’s not a bad thing, but it does mean the end of the Democrats. I don’t think he wants that.
However, if he loses those races, then he can tell them that he keeps supporting their agenda,but the bad Republicans are being obstacles.
It won’t be the end of the Democrats, because they will still be elected. They will still have a party.
Republicans will be replaced, a Senate Majority of Democrats means there will be 4 more SCOTUS Justices appointed by Biden.