I suspect Zoro will separate from the crew late in the story to settle business with Mihawk, and then turns up to handle business.
Elbaf
I think Zoro fights Killingham and gaining control of advanced CoC to unleash a gigantic, AoE attack that instantly wipes out Killingham and his giant creations. Picture a Haki swordsmanship feat that completely overshadows Nusjuro's feat Egghead in scale and is stronger than any Kamusari seen thus before (obv not including Roger's unnamed move in his clash with WB in Oden's flashback).
Hachinosu*
I half suspect the Strawhats will go to Hachinosu before Lodestar, and if they do, I expect the Monster Trio to have a massive combined CoC feat. I would also expect Zoro to one shot Pizarro effortlessly. It's possible the Big Mom Pirates also show up at this time, and I could see Zoro briefly clashing with Katakuri.
Lodestar
I expect an exciting run in with the Red Hair Pirates in which Zoro fights Ben Beckmann to a respectable stalemate "greeting". I expect a talk and flashback sequence from Shanks, after Blackbeard shows up with an armada. An all out war follows of the Strawhats, Red Hair Pirates (and possibly some of their allies) versus Blackbeard Pirates leading hundreds of crews/thousands of pirates.
I believe this could be the battle Oda promised would put Marineford to shame, and if it does, I could even see Knights, Elders and Admirals getting involved.
Whatever goes down, I expect Zoro to be comfortably beating Shiryu and/or Nusjuro (or stalemating one of them at worst) and having to retreat when Luffy is defeated. Shanks covers their escape and dies to a cowardly attack by Blackbeard, who takes the lead in the race for the One Piece after his victory.
The Strawhats have to tend to their wounds, and in the meantime the WG effectively blockades Lodestar and the path to Raftel.
The Strawhats may have to call in allies of their Grand Fleet and elsewhere to punch through, which will likely take some time.
It is at this time I could see Zoro leaving to challenge Mihawk in preparation for their final battle, staking his life on evolving in such a manner his crew will never be defeated again.
Zoro becomes WSS and shows up in time for the war. I could see him fighting an Admiral beforehand, but I expect his final fight to be versus an immortal Shiryu with Nusjuro's powers after Blackbeard has defeated Imu and taken his powers.
TL;DR -- Killingham > Pizarro > Beckmann > Shiryu I > Nusjuro II > Mihawk II > Shiryu II