If you are asking whether the airlines will eventually release L/D/A inventory, thereby clearing the waitlist, rather than see a cabin go with empty seats, my answer would be that it depends on the airline. I think, based on my very limited experience with waitlists, that IB, LA and QF are quite capable of flying with empty seats and not budge an inch. AA seems more accommodating.

By the way, a forum search for 'waitlist' will bring several threads on the subject.