Speaking to Rock, Paper, Shotgun, a SimCity developer revealed that engineering a single-player mode for SimCity would require minimal effort. This statement contradicts statements by EA and Maxis studio head Lucy Bradshaw, who claim the game "offloads a significant amount of calculations to the servers". The anonymous source explains the servers are only handling the social aspects of the game plus saving the game in the cloud, other than that they're not doing anything that can't be done off-line. He (or she) also mentions that "it wouldn't take very much engineering to deliver a limited single-player version without all the nifty region stuff."
So what are the servers doing? Well, alongside the obvious, of being involved in allowing players to share the same maps for their cities, and processing imports and exports between them, they’re really there to check that players aren’t cheating or hacking. However, these checks aren’t in real-time – in fact, they might take a few minutes, so couldn’t be directly involved in your game.
“Because of the way Glassbox was designed, simulation data had to go through a different pathway. The game would regularly pass updates to the server, and then the server would stick those messages in a huge queue along with the messages from everyone else playing. The server pulls messages off the queue, farms them out to other servers to be processed and then those servers send you a package of updates back. The amount of time it could take for you to get a server update responding to something you’ve just done in the game could be as long as a few minutes. This is why they disabled Cheetah mode, by the way, to reduce by half the number of updates coming into the queue.”
Clearly an offline game that included a single-player simulation of the region system derived from multiplayer would be more challenging to develop, but our source assured us that it was far from impossible.