Fortunately this won't be the end of the world, as quite a few states and localities now have net neutrality laws of their own, which would presumably go back into effect if it were deregulated at the federal level again.

Of course, the FCC could presumably create a rule that explicitly allows ISPs to do non-neutral shenanigans, and then the DoJ could start suing states, saying the federal rule preempts them. Not sure how that would pan out, though I'm sure the current composition of SCOTUS would be fine backing the FCC in this case, if the challenges got that far.

I'd say 50/50

By "they" you mean voters. This policy isn't top priority for very many voters, but the battle lines on this are clear. Trump will overturn (he already did once). Biden will protect it. A vote for Trump is a vote to overturn.

If there is a new administration, close to 100%.

Depends on who controls the US Senate, presumably!