The GOP should really fear a Warnock vs. Loeffler runoff. If that's what it comes down to then that would favor the Democrats. I can't imagine an easier incumbent to run against in a state that still tilts (Republican) red.
I think it would depend entirely on who's President-elect (see: 2008), though candidate quality would favor Warnock.
That's definitely true, but if it's high-propensity voters like the elderly or educated voters that are fueling Democratic success in the polls, then I don't think that off-year elections or runoffs are going to favor the GOP to the extent that they did in 2010 or 2014.
I also don't think it's a given that Trump-supporters are going to be as eager to get out and vote once Trump has lost. I think that the loss of Trump will result in a huge crisis of identity for the GOP, but who knows what the immediate electoral consequences of that will be?
