The irony of that situation is that if Trump were to refuse to leave after the new president is sworn in, he would find the gun barrels of his secret service detail pointed directly at his head.
If he still refused to leave, he would be shot dead on the spot.
Even if he agrees to leave at that point, he would be met at the exit by the United States Marshalls and arrested.
He would face felony trespassing, reckless endangerment, terroristic threats, threats to the president and probably several more charges.
He would die in prison.