You can activate vacation mode in order to not worry about losing your cities while away from the game for a while. To do this, go to "Settings" and then to "Vacation mode".
You can use 42 free vacations days per year. If that is not enough, you can buy an additional 14 days with gold.
Please note that your vacation mode will only start 48h after activation. You will still be vulnerable during the first 48h, so plan well ahead!
Vacation mode applies to all game worlds. For more detailed information on the vacation mode feature, please check out our wiki.