It's meant to be a fairytale, not a morality one ;) I rather feel those require some sort of happy ending - even if I have to employ a bit of magic/deus ex machina to get there, haha.

In the original telling (where Fíli aged ~10 tells the story to distract the other children from the adults worrying about a mine collapse) I touch on the idea that it's believed that fiddlers of great skill as well as those with grey/water eyes are descendants of Fasta/Nykr, which suggests that they've procreated (and that Nykr and Fasta were not biologically incompatible, I guess) which I feel means Aulë probably had a hand in shaping Nykr's people - a not-quite-prototype, perhaps?