If scotus determines that states violated their own election laws and/or there is evidence of fraud greater than margin of victory then the electoral college certifications for those states where never valid. Which means Biden did not get 270, therefore the inauguration could not be considered valid,

I would think that scotus would probably then have to call for a house delegation vote to occur, which would have been the correct procedure if neither candidate received 270 EC votes on Jan 6 (Trump wins this way).