Here is my grand theory: Yamato and Tama will see Ace and Whitebeard's graves on Sphinx Island. Before anyone comes at me, its not confirmed but there is heavy suspicion that their graves are on Sphinx Island. It makes sense for these two characters to venture with the crew for Sphinx Island, they both are similar in character and both had bath interactions with Ace. Its natural for them to see him once again. Yamato will venture with the crew to Elbaf and Tama will go back to Wano (somehow). This is where it gets interesting, Shanks will be waiting for Luffy on Sphinx Island, and this is where astronomical revelations are to be made for the future of the series going onward. I dont to critical analysis of the series or Theory bullshit, but this is how I think the Yonko saga ends and the Final Saga commences.