User blog comment:AYET/(95) The Last Shichibukai/@comment-4899461-20130325155251

Marco is ultimately a strong guy. The Whitebeard Pirates are a strong crew. Yes, it would be hard for them to keep all their territory from a force as powerful as Blackbeard & crew, but I don't think they would be so desperate that they would need to join up with someone or die. In order to hunt down the remaining WB pirates, they would need to send Admirals (plural), many Vice Admirals, and some Shichibukai after them, and frankly I don't think the World Government considers the remaining Whitebeard Pirates to be a threat worth that kind of response.

I think the most likely future for Marco is that he has become an ally of the Red Hair Pirates, much like the Whitebeard Allies were an ally of Whitebeard. He's not technically part of their crew structure, but in a way protected by Shanks.

And the info on the new Shichibukai did not come from the actual movie of Z, but the special volume that came with it. It's in the part about the timeline of Zephyr's life.