Safari does not restore tabs / not Resuming
It's not a setting in Safari, but a general setting. Go to your System Preferences &lt; General and make sure Restore windows when quitting and re-opening apps is checked on.



But you can install some 3th party apps too.  


There is SafariRestore, which will basically do the same. But you have to disable the Restore windows when quitting and re-opening apps on the screenshot above!
You can also add the Sessions extension to Safari which will do the same.


I haven't any experience with neither of these apps, so please let me know if it works out!