If he wins we'll get four years of him behaving like a wannabe tinpot dictator, stacking federal agencies with conservative activists and cronies, running his DOJ like Ken Paxton, being reckless with foreign policy, and possibly crashing the economy. See pre-10/7 Netanyahu. Expect the next four years to be a blue tsunami that makes his first term look like a ripple by comparison. He anoints his VP or one of his kids as his successor in 2028, who get blown out 2008-style.
If he loses, he'll spend the rest of his career ranting about how he was robbed again.
How does this in any way answer what the "post-Trump GOP" looks like?