I don't know what is your source, but it is the first time I ever read someone saying that Louis XIII could have been borderline crazy. Such a claim is groundless.
The man was a shy inhibited very religious man. Some claim that he may have been a repressed homosexual. But he was not borderline crazy.
Which does not prevent you from developing a "what if Louis XIII had turned mentally insane ?"
Lol indeed.
So Louis XIII does not die in 1643, and say lives on another twenty years, how might this change the situation in Europe? Less aggressive France for a time? More focus on colonial adventures