Ok, here's my worst case scenario, short of some kind of tragedy.
Activision is dumping InfinityWard, sent goons to steal back their source code, Treyarch to take over the series and create the MMO in conjunction with Blizzard.
That's my crazy-ass corporate-shenaniganry prediction, though in some weird way, it doesn't sound all that far-fetched to me.
Edit: Or, and this is the more likely of that situation, Activision is cutting off InfinityWard and sent their goons to make sure that no one steals or otherwise tampers with their property until the terms of the split are finalized. That's typical layoff procedure in these sorts of events.