[Gregstrom]

1. IIRC, there's about a 50% chance it joins you. Otherwise, it probably just pops up in the province acting all cranky.
2. Like other uniques, they come back just fine if the RNG calls for them. I don't know about the possibility for multiple attacks in the same turn.
3. There's no loss of dominion, beyond not getting the pretender's domspread while he's away. The bless stays around just fine. The only penalty is that when the pretender's called back he loses one point in all magic paths, and he'll most likely have a couple of afflictions.