We can get back the data set from the Back up taken already. If back up is not taken then the problem araise. For every user one JOB will be running in the background automatically as soon as we log into the mainframes. It traces or logs all actions that we performed through out our active time in Mainframes. With the help of that log file the administrator can trace the deleted dataset and get back the contents of dataset. But I dont know the actual process used there.