From what I've been told, the game would be significantly less functional as a single player game right now given that it's orientated toward cooperation between cities.
They could put in AI players or change the mechanics, but I honestly don't think they're going to do that, especially since I suspect they made it so heavily multiplayer oriented, not because they believe a social multiplayer game to be the way of the future, but in an attempt to curb piracy.
As far as I know, there's little several players can do that one can't. It's already possible to set up private regions, playing alone and alternating between cities without ever inviting anyone else (kind of like SC4 worked). The functionality's already there. Sure, there's no realtime cooperation since one person can't manage multiple towns at the same time, but that's not a crippling detail. Most of the work this hypothetical patch would require concerns bringing a bunch of currently server-side processing to be done locally.
Whatever the resource requirement (which should be nowhere near excessive), it doesn't really matter if it's not ideal from the business standpoint. It's their obligation.
Hell, they're even offering a free game to everyone who bought SimCity right now, to compensate for the ongoing server troubles. That shows at least a shred of ethics and responsibility, and it's not earning them any extra revenue, that's for sure. So while demonizers might argue EA cares about nothing but profits, consumer confidence is another important factor that must be cultivated if people are to buy your games in the future.
Ultimately, none of us can be certain about this matter. These hybrid social-singleplayer games, like Diablo III and now SimCity, are just starting to crop up, and there's just no precedent to be sure what'll happen to them in 5-10 years.