If a noble is in his own region, or if any noble is in any region that belongs to his realm, he can't be captured, unless in battle, or he tries doing something like infiltration or trading. Also, you can't capture nobles outside of your realm's regions, unless in battle, infiltration, or trading. I asked.
So I'm not sure what, if anything, the estate is supposed to do. He can't be captured unless he's not part of the realm, in which case he wouldn't have an estate. But it might work if we apply family homes. Certainly the family would shield a noble on the run. Figure out where the character's family home is located, and no matter what, that acts as a safe spot.