No. No. No.
It is not all gone. It might be there somewhere.
Unless the person have run "Disk Sweeper" or any other program wich overwrites the disk so many times that the data get unreadeble.
Anyway: The bits and bytes of porno is still on your hard disk. Just not visible. To see and recover the files you need a recovery program.
There is several out there. When i deleted 50Gigabyte of home-made-videos i recovered them with a program called: "Filescavenger 3.0"
All files recovered, everthing just fine. It costs 45US$.
But: If you use your disk and fill it up. the data will overwrite the "porn" making it nearly impossible to recover. So keep your usage moderate and try to run a recovery program.
You can find FileScavenger for example here:
http://www.snapfiles.com/features/filescavenger-811-421200.php