What if there is new ESC button AND pause button ? With pause you can only pause and un-pause. And if you click/press anything during the pause it will un-pause...
If you're concerned about players seeing around while paused you could probably but some kind of background while in it. It would not prevent hardcore player escaping death (although nothing prevent you to bind alt-f4 to something) but could be a good workaround. Just throwing a random idea.