What happens to Tideturner's trigger if it is returned to hand (gusted) after being flipped from facedown? Does the targeted unit still move?

The targeted unit does not move. When Tideturner is played from Hidden to the battlefield, its play trigger goes on the chain and you choose a target. If the opponent responds with Gust and returns Tideturner to hand before the trigger resolves, the trigger still resolves but has no effect. When the trigger tries to reference Tideturner's 'original location' but Tideturner has changed zones to a non-board zone (hand), that information is no longer available. The check returns 'null' and the instruction to move the chosen unit 'to my original location' is ignored. The chosen unit stays where it is.