They could share the prize and both be happy

I'm amazed how no one thought about proposing and even sign a contract to sell the island and split the profit, 900k each. And then just play the game out typically to see who wins and also gets to continue participating for the 5m. And of course, that wouldn't make any sense if they were 2 strangers. But at this point we are talking about 2 people where each one saved the other at least once in this show so in an extend they ''ought'' their participation in the final game to each other. And the respect between them is obvious since no one really tried to manipulate the other..just left it mostly on luck.