Bannor stuck in crusade?

In my current game, I've utterly crushed Decius for daring to declare war on me. He has one city left, and I'd really love to offer him a chance to survive as my vassall - playing amurite, I like to demand that they give their palace mana to me. But he seems unwilling or unable to switch out of crusade, so I can't offer him that.

I guess he just sits in his only remaining city, surrounded by enemy troops, giving rousing speeches to his people? (city is down to size 1, I've placed a few units around the city so it can't work its tiles)

My question is, will the AI ever switch out of the crusade civic? And if not, where should I post a suggestion to add that in a future patch?

Yes, the AI often gets stuck in crusade and refuses to get out, it's a known issue. You'll probably have to knock him off. Alternatively, it's very easy to modify the XML so that crusade doesn't disable diplomacy. Look in Assets/XML/Gameinfo/CIV4civicinfos.xml for the crusade civic and set <bNoDiplomacyWithEnemies> to 0. This shouldn't break your save.

The base game is not being developed anymore I'm afraid (and hasn't been for a number of years), so there's no point posting suggestions in the main forum. You can head to the modmod forums and post your suggestion there: as an AI issue, the MNAI branch maintained by Tholal may be the most accomodating.

Is being stuck in crusade actually an issue? Crusade, to me, sounds like death or victory and the Bannor sound like they are leaning to death.

In any case, another option is to join the Overcouncil and then arrange for an armistice via the Overcouncil.