I'm pretty sure if GTAIV has very good online play, then the MTA Team will just move on with their lives. Get a well payed full time job as computer stuff, and we'll still enjoy playing GTAIV online, as they will, but without working on it. Haha maybe even they get jobs at rockstar north, making the online mod, for GTAV.
And if not, they could make other non-online games online. Rebuild the GTA2 online mode, maybe (cause it sucks), I mean GTA2 is free and rockstar website, that'd be awsome to play wiht 30 people.
And if not not, then they'll keep on improving MTADM, I'm waiting the release just as much as GTAIV, its gonna be huge, it looks extremely proffesional. We/They will have somthing to do.