The Republicans will be all too busy backstabbing each other for the foreseeable future in such a scenario. Trump is in the position he is in now because a majority of GOP voters have a stupid fucking cultish worship of him and nobody else. They tried pushing for other less erratic GOP candidates, but they had managed to brainwash their moronic voters so effectively that they are no longer capable of worshipping anyone else but Trump.
As soon as he is gone, it is going to be a free-for-all among the Republicans, an absolute clusterfuck of a fight to become the next Trump and Vance is not going to be even remotely close to being a candidate for that. He is Trumps pick because he is a spineless vapid non-entity with even less brains than Trump himself. He will not be in a position to do much except getting betrayed by his own party for the rest of the term.
Trump doesn't want the US to be treated fair, at best you would have to be extremely naive to believe that nonsense claim by Trump. The US was already treated more than fairly. Trump destroys all previous foreign relationships the US had in favour of a malfunctioning bully method where he wants it all (but in reality it results in him getting nothing).
In short he is applying the bully method of his failed career as a businessman to the US, where it is even less effective.