The best thing to do is make a Clone of your system to an external disk. Use Carbon Copy Cloner or SuperDuper.
Then if they wipe your internal drive, you can boot from the external and clone it back to the internal.
Yes, you download it from the link provided above. Move it to your apps folder and then run it. You select the source (Macintosh HD) and target (external disk). Then you hit the clone button. This will make a bootable copy of your internal disk on the external. You can try out the clone after you make it by holding down the OPT key at boot between the startup sound and the logo with pinwheel. I will give you a selection of bootable drives. Select your clone. If everything checks out, reboot from internal.
The image above is slightly different with the latest version of Carbon Copy Cloner.