General Manager of Maxis emeryville studio Patrick Buechner has posted a new blog announcing that Sim City offline single-player mode is on the way.
Check out the official Sim City blog to see the full announcement. All previously downloaded content will also be accessible in the new single player mode and you will be able to play the game Offline by yourself, with the ability to save and load at any time.
Also, with the new offline mode, modders can finally make modifications to the game without affecting the Online version. There is currently no planned release date for the update. Also check out the new Engineering SimCity for Offline Play blog that details how the game has been re-coded for Single Player.