I agree, and he clearly stated many times that everything is pointless if he can't even help his captain.
But the complicated point is: if all of this is true, then he simply won't fight Mihawk. Because I don't see the story going from Luffy becoming pirate king, and them being the most infamous crew in the world -> to a Zoro vs Mihawk.
Maybe at the end as a flash forward to all the characters in the future - mangaka do this a lot. But as a full fledged battle...? I don't think so. What would the others be doing, sipping cocktails?
I could imagine an ending with "Zoro became known as the world's strongest swordsman after infamous crash with Mihawk at xx island, where Mihawk acknowledged him"
I can see that happening however, many fans will not be satisfied in Oda off screensthe battle.
I believe a couple of the SH will only accomplish their dreams after Luffy becomes pk.
Brooke's dream of meeting Laboon can only happen after Luffy becomes pk
Nami's goal of drawing a world map can only happen after Luffy becomes pk. Mind you, at the moment, the SH have barely explored the world and by the time Luffy becomes pk, it would still be the same. Look at paradise, the supernovas used different routes to get to a body, meaning that there are multiple areas the SH have not gone to which means they will need to visit them for Namito draw the world map.
Chopper's dream of curing all diseases. He can only achieve this by traveling the world and curing the people. Only achievable after Luffy becomes pk.
Franky's dream of creating a ship that can sail the entire world. Only achievable after Luffy becomes pk.
So it is not like they will be doing nothing after Lufy becomes pk. They will continue sailing the world, will be the strongest crew in the world thus will have the freedom to sail everywhere and accomplish the dream ofthe different SH that require them to sail the entire world