True. If all of the Democrats voted as a bloc, then they could get rid of the filibuster and do whatever they want. If anything fails to pass, then it'll ultimately be due to a bipartisan willingness to let it fail.
Exactly what agreement McConnell and Schumer reach on the Senate rules for the next 2 years will be telling. They haven't reached a deal yet, but it sounds like Democrats are willing to give Republicans a lot of power, and McConnell is even pushing for guaranteeing that the filibuster is preserved.
My guess is that Schumer wants to keep killing the filibuster as an option so he can claim Republican obstructionism as a reason to need to kill the filibuster, and put pressure on Manchin to vote in favor of killing it. Schumer is up for reelection in 2022, which includes a primary race. It is rumored that AOC may run for Senate. It is possible that putting Sanders on the powerful Budget Committee is an effort to try to get AOC to not try to unseat Schumer in the primary.
They’re not going to have the votes to kill the filibuster - Manchin, Sinema, and co are going to stop that vote because they’re all people that convinced Republicans to vote for them because they were going to help real bipartisan change happen in Washington DC.
If it happens and they get away with it, then so be it. But I expect that they’ll probably get told by their voters that they’re not going to let that happen (or at least they’ll punish them during their next election)