I think it's a good idea. An option to leave with fiefs if you have high relations with the ruling clan, or some other way would be good.
The alternative often creates a sudden power vacuum when the player goes to war with thier prior faction and is forced to beat them into submission.
You can pay for peace but often the price when you dump a faction is unreasonable high at first, so it make sense too at least defeat the faction until you've made enough money of loot and ransoms to cover the peace. The damage the player can do to a faction can really throw of the power balance in the world, especially if it's a more vulnerable faction (Empires, sometimes sturgia) who's been depending on the player for protection.
Thanks, yeah, I think it's just logical .... (Plus it could only benefit the gameplay experience).