Can I offer a slightly different approach? Before I get crucified: Mihawk is the world's strongest swordsman.
Nothing is impossible with Oda, if he made an unlikely team of pirates fall from the sky to Marineford, he can make Mihawk theoretically fall in Zoro's lap from a cloud. Times are uncertain as we don't know what Mihawk's next move is, and he has to make some sort of move - or forever roam on his little boat alone.
Now listen why this fight is unlikely:
1) Zoro and Mihawk spent two years training together. So, safe to assume they fought together every day. They know each other's strength levels perfectly. Zoro, THE PUPIL, is probably still weaker than his master, as not a lot of time went by and he had 0 challenges since then. So it makes no sense to turn around now or in three months and fight Mihawk when he made no progress since then. It would be very anti-climatic. Further along the story, in a few years OP time, sure.
2) Mihawk himself noted that he found a cause greater than his own ambition. Which is true because Zoro gave up even his pride for Luffy and Luffy's dream. IF you think about it, none of the Straw Hats really talk about their dreams anymore past time skip, they all decided to give their all to their captain. So Zoro also decided this was what he was going to do, he's not going to go on about his ambition anymore now. Maybe in the far future they do crash, but again it makes no sense now. You don't have to fight sameone to surpass them in skill.
3) People keep mentioning chapter 51, yes, that is where the ambition got fired up, as well as the setting for their future crash. But why is it impossible that between this and chapter 597 (not bothered to check) when he became his teacher, which is 13 YEARS apart (not even Oda could have predicted the manga would last more than a few years!!!!!), Oda might have changed his mind and decided to have Zoro cast his ambition aside to learn from the world's strongest swordsman? Thus making it kinda pointless to fight now as there is very little tension between these characters and mutual respect instead?
Now, if Mihawk does by some plot twist end up being his opponent, it will be interesting. Just don't see it happening, especially as final.
Disclaimer: please don't repeat like a parrot about him achieving his dream. I just spent five minutes talking about him postponing his ambition for the time being.