How to enable offline mode in SimCity
The trick comes via a post on Neogaf, check the link for more information but basically you need to remove the following lines from the code:
kNoRepeatNetworkAlertSeconds : 15,
kNetDownForceQuitAfterMinutes : 20,
The exact section of code can be found here. Whilst this will allow you to play offline, it doesn’t allow you to save, although apparently that ‘fix’ is coming soon.
Tamper with code at your own risk.