Due to a bug with the horde quest Coward Delivery... Under 30 Minutes or it's Free you can keep the alliance deserter after you were supposed to hand him over.
The trick is to mount up right after you signaled the Alliance. This will ensure that the deserter will not follow the paladin'ish knight, but stay behind as your companion. May require several tries to work (disband quest and try again).
It will hang around with you even after you turned in the quest. You can even zone out, and it will still follow you around. Logging out doesn't cause this "pet" to despawn either. It will follow you around until you summon another pet.
If the pet does despawn due to you flying away, all you have to do is relog to spawn it again.
Have fun with your Alliance "pet" /pat :3
Cheers
Screenshot of me and my deserter chillin in Org:
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