Usually the hackers who are stealing or copying the files from the computer hard drive are interested in stealing the data repeatedly especially if it has some commercial value and can be sold to the enemies,
So in most cases, they are not deleting the files after copying them, since the victim wil become suspicious
Only in case of citizens who are targetted for identity theft like the domain investor, the files are deleted from the hard drive remotely by the hackers
So all the time and effort of the person creating the file is wasted.
Radiation is used to destroy the memory cells, and in some cases, also the data stored on the computer hard drive, pen drives.