Update 10 will allow players to finally play offline with access to all of their previously downloaded content in the new single player mode. Which the developer was exploring the possibility of offline play back in October 2013.
While EA has not revealed a full list of details for the update, it did note that single player campaign saves will be stored locally and not on the cloud. So players will no longer be required to have an internet connection when playing the game.
Source: http://www.simcity.com/en_US/blog/article/simcity-offline-is-coming