In theory there's no limit. Practically speaking, though, I would split it up. I've been doing a "Campaign" in Roll20 equal to more of an "Adventure" in the "Adventure Path" sort of epic campaign. There's a mechanism where you can Copy/Extend the Campaign when you're ready to start the next adventure, so you can copy over the players, macros, decks, chat log, etc., and just start with new pages.
