What would happen if you somehow killed the derse king before the reckoning? Or stopped the prospit king from dying? Or just fucked with any of the derse/prospit royalty before/in a different way than you were supposed to?

Players aren’t supposed to interfere with the war until after it’s over. If you stop the Reckoning then you’ll create a doomed timeline since the Reckoning is necessary for the players to be sent back to Earth in the first place.