Most things indicate that the Alliance won the Darkshore Warfront. Nathanos is no longer at Darkshore (having headed back to Zandalar before the Battle of Dazar’alor, and then we’ll see him for Nazjatar before he goes back to Orgrimmar, and he doesn’t show up in the Alliance version of the Darkshore Warfront, either). The Horde’s version of the warfront is set right after the Alliance intro questing since the Horde has to save Belmont, and since that’s always the case and generals don’t change like at Arathi it would seem this is a gameplay mechanic like repeating dungeons rather than battlegrounds (Belmont also doesn’t show up in the Alliance version of the Darkshore Warfront, so it’s not like the Alliance players recapture him every time, either).
And even outside the Darkshore Warfront we have support that the Alliance won:
I think that canonically the Alliance side of Darkshore questing has to come after the Horde, because the Alliance fights an undead and corrupted version of Ivus after he was killed by the Horde during their quests.
So that’s in-game evidence that the Alliance is winning in Darkshore.
Most peculiar, though, is Blizzard made a cinematic for the Night Elves winning Darkshore, and just didn’t put it in the game:
A New Hope
Witness Tyrande's address to the kaldorei. A level 50 Quest. Rewards Nightwreathed Egg. Added in World of Warcraft: Battle for Azeroth. Always up to date.
Even more oddly, the quest “A New Hope” is technically in game, just wasn’t made accessible. However, if you have a Nightwreathed Watcher collected in your pet battle journal it will tell you there are three sources for it: Grimhorn for the Horde, Orwell Stevenson for the Alliance, and the quest “A New Hope”, I guess as leftover data in the game that they missed removing.