Does Ctrl+Alt+Backspace not kill X any more (assuming you’re using X)?
Does Ctrl+Alt+Delete reboot the system from a graphical desktop? Or is that only from the virtual consoles?
I wonder if locking the session would have stopped it as well. I doubt the Alt+SysRq combos would have been useful since other random input was happening at the same time (unless the next keystroke happened to be an I, U, or B).
It never was.