As in life there are no guarantees. If the engine is run as per the book you generally don't have problems. As I said before this is really not a lop issue. The engine is designed around the px in the chambers. The bearings will fail before the head. Rapid cooling is something else which is hard on an engine. Flight schools and meat bomb aircraft suffer the worst cracking. That's why you have reduced cruise power settings.
So which will crack first. If you have an aircraft that is px to a max diff of 8.5 psi and you fly it un pressurized will it crack more at max diff or with no px in the cabin.