With the cues and hints Embala and I gathered in the Shadowcrest thread, I feel reasonably safe to assume, until the Pinis say otherwise, that the ghostly elf on the left is PIRN, Darshek's father - and the one who presumably left him his trademark headband. Moving, when you consider that...
"Darshek barely knew his father, Pirn." (Longfin to Krill)
"Pirn will be happy to see the grown up son he last saw as a newborn pip." (Salt to Longfin)
... which is like saying he only knows his father through the tales he's heard, his headband, and if you'll forgive the Pixar pun, his "spirit of adventure" (at least I like to think it came from Pirn. Although Longfin *was* pretty brave, when pushed by Krill... but Darshek is such a free spirit, bold and daring, it must come from somewhere!)
So Pirn must have died when Darshek was a little baby, some time during the 9000 years of the Disappearance. We know that he wasn't killed by humans, because Coral (and Haze and Farbright shortly thereafter) were "the first" WaveDancers slained by mankind. And it was not from illness, either - since Skimmer was a pretty formidable healer who knew only one failure (that would be the Broken One).
But between bellyrippers, daggerteeth and goodness knows what other sea-predators roam the waters of Above, there are many ways he could have met his death. Poor Pirn
I wonder if he was lifemated to Longfin alone, or if he, Longfin and Shadowcrest were part of a threemating? Personally I'm all for the thought that they were a threesome. Why, otherwise, a dying Darshek would see the ghost not just of his father, but of Shadowcrest?*
(Of course, given Pirn died when he was so little, he could have been raised by Shadowcrest and Longfin... but to me, something in the way they're reaching toward Darshek suggests a deeper closeness...)
* Of course, he sees Stormsong, Drift and Fairshell too. But the ones we see through his eyes, clearer than all the others (who are only named) are "his mother's lifemates" and I like to think it's not a coincidence