Even if it required impeachment, Congress (under pressure from a population with irrefutable proof of a stolen election) could remove Biden, Harris, Pelosi and on down the line until they reached someone who was not involved with the coup. Then it would be up to Congress to decide who'd take office, and the obvious answer would be the one who rightfully won. He could, I imagine, choose whoever he wanted as the VP with full support from Congress as Pence was likely playing for the wrong team.