According to this (http://www.reddit.com/r/SimCity/comments/19xx7d/trying_some_technical_analysis_of_the_server/ http://www.reddit.com/r/SimCity/comments/19xx7d

According to this (http://www.reddit.com/r/SimCity/comments/19xx7d/trying_some_technical_analysis_of_the_server/ http://www.reddit.com/r/SimCity/comments/19xx7d/trying_some_...) the game runs completely fine without being connected to the server, just all the mp features won't work. All the server does is handle trading, leaderboards, regions and validation etc