[Aiwendil]

Yet he and his family would remain cursed

I do not think that Tolkien would suggest that this might not occur, that Turin's "doom" would not find him if he did or refrained from doing anything. Gwindor's prophecy is a late addition to Turin's tale. I do not think that it does anything for the story; the tale is equally tragic if Turin ignores Gwindor's dying wish that he rescue Finduilas without linking the rescue to an undoing of his curse or doom. To the contrary, to suggest that a simple "good deed" could contravene Morgoth's curse is a bit too blithe a solution. And what of the fact that even Turin's attempts to do good are turned awry by the curse? The idea that rescuing Finduilas would avert Turin's doom simply does not fit.

If Tolkien had ever assembled the "final draft" of Narn i Hin Hurin, I suggest that Gwindor's prophecy would not have been included; the earlier iteration of his dying words would have been used. Tolkien was simply too careful an author to let something slip in that seems to run contrary to the themes of that tale.

I disagree.

I think that this "what if" scenario touches on the interesting questions of just what Morgoth's curse was and how it worked. In particular, there's a fate vs. free-will ambiguity in the curse, and I think that your analysis (though well-thought out and perceptive) considers the matter only from one side.

An interesting question to consider as one reads the 'Narn' is to what extent Turin's misfortunes are the result of Morgoth's curse and to what extent they are the result of his own decisions. The interesting thing is that almost every time something goes wrong for Turin, it seems (at least on one level) to be the result of his own actions. The death of Saeros, for example, occurs because of the particular way in which Turin chooses to deal with his anger in that situation. When one considers that incident (or indeed any of Turin's misfortunes) alone, one is hard-pressed to point out exactly where the Curse plays any role at all. It looks like the characters involved are all acting of their own accord and not subject to any external constraints or influence. On the other hand, when one steps back and looks at the whole story, one does undoubtedly see Morgoth's curse at work. Moreover, we know that Turin's life is dominated by the curse because we see Morgoth pronounce it at the beginning of the tale. It may seem difficult to reconcile these two interpretations; I think the solution is that we must not attempt to reconcile them at all, but rather accept that, strange as it may seem, each is true in its own way. This is, I think, similar to the ambiguity between internal and external evil in the One Ring.

So it is also with the issue of rescuing Finduilas. Though Turin's choice not to rescue Finduilas can perhaps be put down to the dragon-spell, he apparently chooses (of his own unconstrained will) to lift his visor and look Glaurung in the eye. Yet, what looks like (and probably is) a free choice on his part turns out, in the long run, to be part of his doom.

I suppose another way of saying this is that somehow Morgoth's curse is manifested through Turin's choices. His failure to rescue Finduilas is, then, part of his curse. It makes little sense, to me anyway, even to posit that, had he rescued Finduilas, his curse would still have found him. For the curse is (in part) that he failed to rescue Finduilas. One can easily imagine a lot of hypothetical worlds where Turin's lot is happier, had he made this choice or that choice differently. The curse is that he didn't make those choices differently.

What does this matter? It may seem that I'm only addressing an issue of semantics, but I think there's more to it than that. It is integral to the effect of the story, I think, not only that Turin make the wrong choices, but that he regret those choices. The tragedy that follows from his failure to rescue Finduilas is, I think, all the more acute if we can see a way in which it might have been averted. If we simply shrug and say "Oh well, things still would somehow have gone badly if he'd rescued her" then we lose some of the tragedy of his failure to do so.