[Numenorean]

Great thread and posts. Maybe the core of this question - due in no small part to the magical subtlety of Tolkiens words – depends entirely on the beliefs of the reader, or as Guinevere states:

Much depends on the definition of "love".

Like others, I have always got the feeling that Túrin would indeed have reciprocated Finduilas’ love – of the kind she wished it to be - had it not been for his honour bound friendship with Gwindor. To me it seems like another fey strand of the curse that haunts Túrins every turn: he is brought to the refuge sanctuary of Nargothrond (and Finduilas) by the only one of that realm whom he owes his life to, Gwindor, who just happens to also be the one Elf that was romantically involved with Finduilas in times past. The seeds of a fragile and doomed triangle between the three are sown from the beginning, masterfully shrouded in Tolkiens gift for pathos.
For me, Aiwendil rightly says that none...

of the three is quite able to see the entire truth of the situation

- Túrin least of all it seems, as he says of himself, with the truth seeing eyes of his imminent death near the end of CoH: “For see, I am blind! Did you not know? Blind, blind, groping since childhood in a dark mist of Morgoth”.

Over in the excellent Translations from the Elvish – Narn i Chîn Húrin thread http://forum.barrowdowns.com/showthread.php?p=522376 by Findegil, I saw these wonderfully poignant lines from the Lay that (to me) echo the subtleties and unspoken passion of the situation:

…of Túrins Sorrows at this time it is told in the Lay:

From woe unhealed __ the wounded heart
of Túrin the tall __ was turned to her.
...
the glory of her eyes __ that gleamed with fires
of secret thought __ in silent deeps.

This also complements what Son of Númenor wrote here:

the Finduilas strand is a 'What if...?' which Tolkien left vague intentionally - another layer of the misty veil surrounding the predestined fall of his tragic hero

As to how could saving Finduilas avert Túrins doom, I’m in agreement with Aiwendil & Guinivere that:

it certainly does make perfect sense to suppose that Túrin would have wedded Finduilas if he had saved her.

Thus altering the fateful path of doom that led him to Niënor/Níniel and his bitter end.

Guinivere:

Gwindor's flash of "foresight" in his dying hour had probably not been explicit. But it is rather noble of him to give this warning and commit Finduilas to his rival.

If only Gwindor had been as noble and upfront to Túrin regarding Finduilas prior to that dark day, things might have transpired rather differently. Maybe such speculation only begs another unanswerable question, namely; was Love the only fate strong enough to defeat or offset the Curse of Morgoth and Túrins doom?