os.pullEvent = os.pullEventRaw
Will stop the terminate event from happening since it is part of the os.pullEvent. Basically your removing os.pullEvent, and using os.pullEventRaw which does not include the terminate event. It does nothing with the ctrl key.
There are no reboot or shutdown events for that to capture and stop. And since it is hardcoded you can not stop it without removing the boot option from the bios.lua.
Only option you have if you can not edit the bios is to place a disk drive with a startup file on in on top of the computer.












