I think it'll be either 54 or 55 Republicans in the Senate come 2023. That hinges on Colorado. That would mean the tipping-point state is the one Democrats lose by the largest margin, which I think is Arizona.
I don't see Democrats losing Nevada or Colorado. Even in the 2010 Wave they managed to hold those States.
In the 2010 NV Sen race, the Republicans ran a really terrible canidate against an entrenched Senate majority leader who constantly won by close margins and the rurals were a lot less red back then for the Senate races. In 2012, Dean Heller managed to held on even in a bad year for the GOP up and down the ballot. In 2018, Rosen only won by 5 in a blue wave year.
