The considerations one makes prior to choosing to do something (supposing these are considerations in order to make the optimal decision for one?s own good) have an effect on the impact of regret felt once said action has been completed. So I wonder: if there?s such a thing as anticipatory regret (you regret something before even doing it and then do it anyway), to what extent does this anticipation of regret weight on the regret you actually feel after completion of an action?
Regret depends on the information you had prior to making your decision ? if you were not aware of possible alternative courses of action, or factors you had no control over affected the decision [i.e. an unavoidable natural disaster] then perhaps the regret you feel is lesser ? I would think this to be rational, for you do not have the same weight of responsibility as you would if you had all your options laid out in front of you. The blame you might feel is lesser. You can experience more regret if you realize that you did not weigh your options correctly prior to the fact or if you did not realize the nuances of the decision about to be made - if you under-weigh regret prior to taking action. Thus, how implicated one is prior to action affects how much regret is eventually felt. 

Go gentle into that good night?
Purity of heart  may be to will one thing, but regret and remorse are biological necessities, and no simple matter. Memory is not a system of file retreival. In a sense memory does not exist at all, it is remanufactured each time through a vast fabric of reminders. Each reminder triggers others that assembled something like the original, but never quite the same (some psychologists insist that they can stimulate exact replication of original experience but do nothing to establish this claim other than to point to the remarkable certitude of this that accompanies it, but this is no more creditable a claim than the now discredited "retreived memory"). Nagging memories assure an extensive reconsideration that may adjust future behavior and, more pertinently, motivate reflection upon the character of one's values, and about the nature of one's place in the world and in course of one's life.
Neitzsche always comes up, like a bad penny. He was merely parroting the ancient feudal ethic that the loser in a joust not resent the spoils going to the victor, or the gambler's ethic that the loser has no appeal. But the notion makes no sense in morality ethics or law. A game of chance, or of arms, does not credit the victor as earning the prize, and the loser has no reason to suppose it does, other than the fantasy of possesing what was not earned. It is the dogma of the winner pressed relentlessly against the reasonable claim of the loser. Remember the line in Romney's campaign about the "politics of resentment"? Those with the upper hand in the world can act in accord, as if efficiently coordinated conspiratorially. Those of diminished resources or effective voice in a real sense weaken their case by acting in concert. And so the elites of the world have a natural social and political advantage that has nothing whatever to do with merit.
Go gentle into that good night? The issue of remorse and regret has tentacles reaching into every nook and cranny of life and memory, and to present it as if it were a simple topic activates those tentacles while obscuring them and their pernicious work on us. 
 
 
 
 

Regret is an essential element to the cultivation of virtue.

There is a false assumption in the "you can't have it both ways" thinking of wanting to undo something regretted. The assumption is that if we change the past thereby giving up something we like about the present, that we would not end up in another equally good or better present. In the example on the show, saving his aunt would mean not having his son, but it DOES NOT mean that he wouldn't have a son that he cherished. The deep underlying assumption in our culture is that we cannot create positive outcomes for ourselves, and that whatever we have that we cherish is an accident. Rather, the positive outcome we cherish is only one of an infinity of possible positive outcomes. So regret away: dream of changing the past, give up what you have, and something else good will come!