A few details have come to light in the question of how difficult it would be to make the new SimCity playable offline, a conundrum that confuses even EA, as they have indicated this would be both possible and impossible. Kotaku writes of pulling the plug on the game and having it play on for about 19 minutes before crapping out, seeming to contradict the notion that a significant portion of the game's calculations are taking place on the server side. Likewise, Notch tweets: "I like how you can keep playing Sim City even when it notifies you that the servers are down. (But I thought it REALLY needed them?)." This plays into a report on Rock, Paper, Shotgun talking with an anonymous engineer the site says they've confirmed worked on the game. He discusses the most difficult part of playing SimCity offline would be how gameplay is based on interactions between regions, but the source says: "It wouldn’t take very much engineering to give you a limited single-player game without all the nifty region stuff." As for the server being required to play the game, he tells them SimCity does no significant game simulation on the server side:

The servers are not handling any of the computation done to simulate the city you are playing. They are still acting as servers, doing some amount of computation to route messages of various types between both players and cities. As well, they’re doing cloud storage of save games, interfacing with Origin, and all of that. But for the game itself? No, they’re not doing anything. I have no idea why they’re claiming otherwise. It’s possible that Bradshaw misunderstood or was misinformed, but otherwise I’m clueless.