Saint Shanks will spend a lifetime impotently losing every major head on war with Teach. He will eventually switch to tricky tactics to sneakily Saint Shank Teach while the latter is in a global war against 1/2 the remaining major global powers.
Teach will tire of Saint Shanks's shit and give him a treaty to sod off forever. Saint Shanks will accept out of practicality but will still grumble about the 1/4 of his territory that he didn't get back. The Saint Red hair Pirates fall into civil war regarding the treaty. Pro-treaty side win, Benn Beckman assassinated, more RHP dead from civil war than from fighting Teach.
The RHP and BBP will then become friendly, Saint Shanks will start copying Teach's mannerisms and their kids will date each other.
This is not peak fiction.