Some states had elections that don't have this sort of taint. Those stand. If SCOTUS renders decisions that affect outcome of election contests, it will be on a state-by-state basis. Up to Congress to deal with the resulting mess, if there is one.
Not the way I understand it.
If one state, or a group of states voting is/are invalidated, then all states are invalidated. Why? Because what happened in those guilty states effects ALL states.
Its called equal protection. That is why quite a few states have enjoined the lawsuits against the offending states..against PA in particular.
Congress will only get involved if PA is ruled invalid. Then the issue goes back to the state legislature to vote for ONE elector to represent that state in the house Of Reps to which the house HAS to vote as the State legislatures direct them. They CAN NOT go off and vote whichever way they want.