Democrats would have likely netted between 4 and 7 seats, enough to flip the Senate. For starters, I'm assuming Loeffler wins the runoff. In your scenario, Perdue probably squeaked by with just over 50%, so Republicans would hold the Senate and Democrats would be far less motivated to turn out. However, they would likely flip GA in 2022, along with PA, WI and NC.
FL, OH and IA would be tossups, but I think Democrats would have picked up at least one, with their best bet being an open seat in OH or IA. Sweeping all three would be possible on a very good night.
Well, considering Dems won both seats after a Trump loss, I have to assume they would also win both seats after a Trump win. So the Senate is 50/50 and R-controlled through Pence unless James won in Michigan (he would need more that just a uniform swing).
A 2022 Trump midterm is probably D+3 as a baseline (PA/WI/NC), so 53D/47R, and even if they lost both GA runoffs, they would still take control 51/49 or 52/48 if Loeffler lost in 2022.
If the midterm was a wave election, there’s a line around a D+8 PV where it abruptly turns into D+8-10 instead of D+3-4. They would need this to be confident in holding the Senate if 2024 is a normal non-wave year (it would be line 2018-20 was in the House because 2024 is an almost automatic R+3-4 with R+8-10 potential).
So it’s either 53D/47R or 58D/42R.
Usually the side that wins in November does well in the January runoffs - just an observation from the last few years. Not saying Dems definitely would've lost, but between Trump not grousing about 'stolen elections' and Dems not having the turnout enthusiasm boost of having just won the state I think it likely that Perdue at least would've won.
Either way Dems would've won the senate in 2022 under this scenario. WI / PA / NC / GA all flip for sure, and OH / IA (w/o Grassley) are two additional options to expand the majority. Most likely Dems end up holding ~53 seats or so coming out of 2022.
