I think every situation is diferent. I've caught fish with a fly in its jaw that I broke off within the last 30 mins. Then theres times where theres no way in hell that fish is going to feed for the next several hours. I think it depends on time of year, the river, the hatch, the water temp. If theres a mid summer feeding frenzy on a sierra freestone water then yes I'd bet you have a decent chance to get that fish again in a reasonible amount of time, If your on a more technical tailwater or springcreek then chances are you had your chance. Yes they wise up to your fly's. When the same thing drifts by dozens of times in the sammer manner then that is abnormal and I think wild creatures such as trout identify things that are "abnormal" in there enviroment, after all I'm sure you know when something isn't right in your home. Just some of my own thoughts.

here is a situation on putah that i have encountered many times before. seeing a fish in a feeding lane and u drift the same flys to them about half dozen times and finally after several drifts one works perfectly and the fish takes the fly. this could be that the drift was perfect or it could just be out of reaction do to the fish seeing the same fly several times (like u made your own hatch). also i have noticed on putah that if u hook a fish and loose it, dont stop fishing that hole right away, put a couple more drifts through, if u get nothing then give it about a 15 min break. either that fish will go back to its feeding spot, or the fish that was behind that one will move up into that feeding lane. this is mostly for putah. on the high sierras, like dr bombay said, it really doesnt matter, the fish are everywhere and they are always hungry.