I imagine that if the leak was large enough I would notice it on the boat when I do my pre dive gear check. If it occurs during the dive I'm sure I would hear or see the sudden burst of bubbles. I always check the pressure between dives, and I was that concerned about it during the dive I have a spare spg at home I could always hook up.
If I ever decide to go the full tech route I'm sure this will change. But I've been doing it since 97, and haven't had an issue.
If anything I'm thinking of switching to doubles. So this ain't be an issue.
**** happens, too many maybes there for my liking.