Yes if you make a new directory within an RGM relationship, it will make the directory if it is not there already

If it is there already, it will use that folder to any new user you add to the distribution list. 

If the folder is there already, it will populate, but be careful not to step on people’s existing folders

If the folder was there, and was deleted, however, it will not REMAKE the folder if it is deleted, it will put the relationship in alert.

The easiest option in that case, If that folder is ONLY a destination folder, then you can uncheck the user in RGM, run full sync, set the Empty Trash option on in Global options, close the console, run the sync and then recheck after the full sync and the folder will be remade and repopulated.

If the folder was both a source and destination folder, recover the folder if possible and then run the Recovery and Migration Manager Tool  to fix the relationships.

Hope this helps