This runs into the "experiencing self" vs "remembering self" distinction. Conceptually it seems very troublesome to perform expected utility calculations on behalf of the experiencing self - the one who would suffer the pains in the above scenario.
From the perspective of the remembering self, pain only matters if it leaves a trace: if you can remember it, or if (unconsciously) it changes the choices you'd make in similar situations in future.
(Think of Sammy Jenkis in the movie Memento who was shown to not be a "true" amnesiac - he avoided picking up toys that had been previously rigged to give him electric shock, even though he behaved as though he had no memory of the past shocks. Yes, this is a fictional example - but despite being fictional it validly highlights a distinction lurking below the surface of the word "memory".)
From this perspective the disutility of the "hell" scenario consists only of the opportunity cost, i.e. while suffering hell you could instead have been doing something pleasant that you'd have remembered afterwards. But deleting the memories, and deleting any dispositions you may have acquired as a result of experiencing the pain, and so on - essentially restoring you to a previous backup - the deleted pain will not count from the perspective of the remembering self.
(Noting the "backup" analogy in the previous paragraph, I have to acknowledge that my intuitions in this may be shaped in part by my experiences playing video games...)
As I recall from my readings on amnesia, having no conscious recollection of events but nevertheless having an unconscious preference (or lack of preference) is fairly common. Essentially patients have impaired declarative (explicit) memory but some spared implicit perceptual and motor memory. So the fictional example of Sammy Jenkis is actually quite reality-based.
What needs to be distinguished in this scenario is whether Omega is only wiping your declarative memory or if he's also going in and getting rid of your implicit memory as well, which takes care of lower-level responses to stimuli that might otherwise cause problems after the event.
So I have a conundrum. Imagine that Omega comes to you and offers you two choices:
First choice: You get a moment of moderate pain, let's say a slap and then another slap, so that your face hurts for a couple of minutes with some anguish. Now after that pain has faded and you still have the memory of it, Omega measures your discomfort and gives you exactly the amount of money that gives enough joy to compensate the pain and then a cent. By construction, the utility of this choice is one cent.
Second choice: Omega inflicts on you hell for a finite amount of time. Your worst fears all come true, you are unable to distinguish between reality and this hell, the most painful sensations you will experience. After this finite amount of time is over, Omega deletes all memory of it and gives you essentially unlimited monetary funds but still, this experience does not quite compensate for the previously experienced hell if you would remember it. By construction, the expected value of this choice is negative.[1]
If we go by expected value, the first choice is obviously better. Of course Omega forces you to take one choice or you will just get hell forever, we want our thought experiment to work. But if we go by the decision procedure to choose the option in which our future self will feel best, the second choice seems better. I have not yet found a satisfying solution to this apparent paradox. Essentially, how does a rational actor deal with discomfort to get to a pleasurable experience?
[1] I realize that this might be a weak point of my argument. Do we just simply add up positive and negative utilons to get our expected value? Or do we already take into consideration the process of forgetting the pain? Maybe therein lies a solution to this paradox.