Pulling out one specific line to call out what I see as a core difficulty here:
They might be fine band aids to get rid of the mourning - but they are not going to produce the experience of triumph a hard won and deserved victory brings along.
But they cannot have that feeling regardless.
You have made clear said that it is
not a "hard won and
deserved victory", emphasis in original. What you are describing isn't them actually having that feeling, it is you intentionally deceiving them in order to make them believe they deserved a flawless victory when....they didn't. They do not realize that what they are feeling is "we got a victory we think we deserved...but didn't"; but that is what happened, and thus their hollow victory seems legitimate.
That, that precise thing, IS a harmful thing as far as I'm concerned. It is telling the player comforting lies. You have told the players that they deserved victories they did not actually deserve. By instead making it so their hard-fought victories are exactly what the dice say they are, you ensure that those players know, without doubt, that when they
feel they've deserved a victory, it is always because they
did deserve a victory--not because you conspired to ensure victory in order to spare their feelings.
The problem with all of these 3 suggestions is that all of them are going to be recognised as the deus ex machina they are. They might be fine band aids to get rid of the mourning - but they are not going to produce the experience of triumph a hard won and deserved victory brings along.
Okay, but now we get to the heart of the matter, don't we?
Because now it isn't about preserving the feeling of a deserved victory. It is about you using a
deus ex machina--which is what ALL of these things are, including the fudged roll!--
appear to not be one, so that the players will feel certain things and not other things. But what is the point of concealing the
deus ex machina, if it is occurring either way? As far as I can tell, the only reason is to make the GM look better, by trying to have her cake and eat it too: she gets all of the benefits of committing a
deus ex machina, without having any of the downsides, because the players have been denied the ability to know that that's what happened.
The pretense is what matters--not the feelings. That's one of the other reasons why I'm not keen on fudging. That nearly-unavoidable element of preserving the GM's image before their players.
In the disintigrate example mentioned above was in a one shot. One of the players characters sacrificed their personal trinket to gatter the dust of the disintegrated person. The group proceeded to complete the mission. There was no rejoicing. The GM put in Elminster resurrecting the dead character in the epilogue. This lightened the mood a bit, but the after talk felt more like a retrospective on a failure than a victory celebration.
Firstly, I'm sorry that that was a negative experience for you. That's not great, and I totally understand why experiencing that would make you feel terribly tempted to resort to fudging.
However...if this sort of thing is going to be such a mega-downer, then IMO the actual error was that you included
disintegrate in the first place. Thus, while an unpleasant experience for those involved, it was a very important learning experience: Don't have magic-using enemies with
disintegrate in a one-shot, because it's much too likely to create a severe downer ending that tarnishes the experience. Using
disintegrate at all involves careful application of various extremely important GM skills, like reading the room and getting the measure of one's players. That's very hard to do in a one-shot format.
Finally, this after-talk thing brings up something very important, and another GM skill that fudging acts as a way to
avoid learning: knowing your players' psychology and personalities. For some players, any death, no matter how well-earned or warranted, tarnishes the experience badly--such that even victory tastes like the ashes of defeat. For others, it would be
putting ashes in their mouths to do this. Deceiving them this way is very much acting against their interests, something they would be openly angry about if they discovered. Why is it better to harm those players in a way they don't know, in order to help the other players in a way they don't know? Again it seems to be that the deciding factor is that doing this deceptively preserves the appearance of the GM being above making mistakes.