Lets say that the crash that killed Patton is avoided, what would happen to his career?
Probably what happened to the other generals: a desk assignment due to drastic reductions in the Army after may 1945. Patton was a great (at least compared to other american generals) "war general", but all war generals have problem in peacetime. Pattons personality would probably stop him from getting any field commands.
Korea could be a possibility, but by then Patton would be 65 years old. Also, Korea was not tank country. And since Korea was an UN operation it would mean coordinating with British, Egyptians, Australians and a lot of other nationalities - not to mention the South Koreas. And diplomacy wasn't Pattons strongest ability.
My guess is that Patton wouldn't fade away gracefully, but become a fairly crouchy commentor on military and foreign policy. He would complain about disbanding the Army, peacetime standards, budget cuts and coddling with communists. If this would damage or strenghten his legacy, and if it really would have some impact on politics, is impossible to say.