he literally left him out of Marineford while the other two were there. So it’s not super shocking he’ll be left out of the next big war against the world government. Or he’ll be retired and just watch it like he did last time.
Marineford wasn’t that big. It was just the WB pirates and their allies vs the marines so they could save Ace.
Law only went in to save Luffy because Will of D. But even he wasn’t an active fighter in the war.
The final war will be a global war. Any character of significant strength will take part in it. Even retired ones.
That is the point of finding the one piece. To trigger a world war.