There is no rational reason to indulge the anti-Trump hallucination of a defeated president holed up in the Oval Office refusing to leave. If ever any president were to try such an inane thing after the constitutionally mandated divestment of executive authority, he or she would be escorted from the premises — hopefully, with whatever dignity could still be mustered under the circumstances.
Presidents do not exercise any control over the electoral process. They may influence it by challenging the results in state and federal courts. But the process is controlled by Congress under longstanding statutory law (found in Chapter 1 of Title 3, U.S. Code). In a nutshell, all state disputes, if any, over election results must be resolved by December 8. On December 14 (the first Monday after the second Wednesday in December), the electors meet in their states and cast their votes. Those votes are certified in the state and then transmitted to Congress, a process that is supposed to be completed by December 23. On January 6 at 1 p.m., both houses of Congress convene to count the votes.
An incumbent president who loses the election may grouse. His supporters may insist that he was robbed. But the states follow their own legal processes to certify the outcome of voting, the electors vote as they must under state law, and Congress tabulates and certifies the result. Regardless of whether we know who won by the night of the November 3 election, we will know no later than mid December, and the outcome will be etched in stone by January 6. Everyone will know that, at noon on January 20, President Trump either will no longer be president or will be starting his second term, as dictated by the Constitution, not by his personal assessment of the situation.