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.
Perdue would still go to a runoff with 49.9%.
