I think this event was meant to break isolated vassals away from a kingdom but it seems a bit sudden to me. I mean, my grandson with 100% loyalty & +5.1 a month suddenly decides to declare independence?
IMHO instead of a sudden declaration the event should reduce the vassals loyalty by 50% and give a -1 to the vassals monthly loyalty. That way it would cost more resources and attention to hold a distant vassal but an extremely loyal vassal would not just take off. Plus, since the event would continue to fire from time to time, the vassal would either have to be allowed to go or be replaced.
IMHO instead of a sudden declaration the event should reduce the vassals loyalty by 50% and give a -1 to the vassals monthly loyalty. That way it would cost more resources and attention to hold a distant vassal but an extremely loyal vassal would not just take off. Plus, since the event would continue to fire from time to time, the vassal would either have to be allowed to go or be replaced.