Is it possible to roll back to the last saved version of a file in mojave?
Normally in most applications when trying to save a file with same name that already exist, your will be asked to confirm. 

Background Save and Auto Save Features in Photoshop CS6

Auto Save, another new feature of Photoshop Cs6,  can help recover your file if your computer crashes before you’ve had a chance to save. To select the time interval for automatically saving your files, select Preferences > File Handling and choose from every  5, 10, 15, 30, or 60 minutes.

Both of these features are on by default. To disable either of these options choose Preferences > File Handling and uncheck Save in Background and/or Automatically Save Recovery Information.

However...if you use the Save command the auto saved version will be replaced/deleted and the process starts over.