So I just recruited the giant companions when got ambushed by a white walker party. I didn 't have obsidian weapons yet and lost and became a prisoner. After I got freed only one giant remained in my party as companion and wun wun disappeared.
Fair enough, I tought, I'll just have to find a traveller to reveal his location and go and get him back. He was in Tyros, at least that is what the guy said but he wasn't there. I am sure that I wasn't late because when I asked again he was supposed to be still there. Then I thought that maybe he spawned back to the cave, so I went there, but the cave despawned.
If I lost a quest conpanion are they lost forewer?