Anyyyhooo, back to Fane
IC, Thomas isn't exactly ecstatic about having the capital of a rebel realm two regions away from his capital city.
OOC, I can see many benefits in Fane continuing to exist. Speaking as a player, I don't really see what will be added to the game by Sirion destroying Fane, beyond Sirion saying, "Woo-hoo, we got another chunk of land". It's painfully obvious that Sirion is already too big. They only have loose control over Commonyr much of the time, even though the regional lord (lady in that case) spends most of her time there. They're getting close to the point where the realm's going to have to split.
It's fairly clear that the next big war is going to have to be either Sirion vs Perdan, or Sirion vs Caligus. Once either Perdan or Caligus wins the southern war, there won't be anyone else big enough for them to bother fighting except Sirion. The same applies to Sirion in the north - the only realms for them to fight will be either Perdan or Caligus. Sirion and Caligus vs Armonia and Eponllyn is a possibility, but it would mostly be a long-range war. But Perdan currently seems to be making mince-meat out of the south.
Allowing Fane to exist will create a more interesting dynamic in the north, and is no threat to Sirion because it's too small. There would also be the potential for Sirion to possibly gain and cultivate Fane as an ally, depending on the approach they took. On the other hand, Sirion can't gain much more land before all of the realms on the continent see them as the greatest threat and someone initiates another mass war against them. Bad news for Sirion, especially because they've been losing nobles.