Effectively nothing, but also everything.
There is no method by which Trump will get into office save for the 2024 election, let's get that out of the way first. While there is some off chance SCOTUS could determine the only possible solution is a new election, it's so terribly unlikely as to be basically impossible.
With that out of the way, what is likely to occur? Well, a massive legal battle which will be the last hurdle for further audits. Arizona de-certifying the election. This move will basically nuke any mandate the admin claims to have from orbit, and provide carte blanche to any state wanting to ignore it. As well as just -nuke- ay foreign policy the admin could do.
From there? Nobody really knows. In an ideal world, it'd be the resignation of both Biden and Kamala, or at least their impeachment. That's unlikely though, and god knows what happens then with an admin utterly stripped of any legitimacy.