I cant imagine him fighting the emperors for sure. He may would try, but at the end, he will need to step down to king or smth, cause the emperors belong to the captain(s). Still assume it will be Luffy, Kidd and Law, which will fight them. Maybe Zoro, Killer and Bepo assist here and there, but the main fight wont be taken by them against the Emperors. Zoro is no doubt the second strongest in the crew and in my eyes the vice captain, but he is and always will be in the shadows of Luffy. This sounds way more negativ for him as it is meant to be, but Luffy will always overshine, like Roger always did with Rayleigh, which makes Rayleigh not less impressing.