Breaking a tributary

[Vohen]

In the game I'm playing right now, the HRE got itself Britannia as a tributary, which formed after the Norman conquest and steamrolling through northern France, Scotland and Ireland.
I'm just a French Duke myself, but I don't want to see the French under Anglo-German rule.

So, there's the question: how or when will this tributary break, if ever?
I've heard that it could break once either the ruler of Britannia or the HRE dies, but they've been together for over a century now and I've personally killed almost half a dozen of their rulers already, and nothing happens.
The tooltip says that they could break if any of them becomes part of another realm, but I'm not betting on that.

I know I could do the succession game and inherit the French duchies from Britannia (or pretty much any duchy I can get a spouse from really) myself, but that OP eternal tributary seems really odd to me.

 

[Rags17]

There are actually three types of basic (ie non modded) tributary - nomadic, lifetime and permanent. Nomadic tributaries last forever or until the suzerain has lower prestige than the vassal or breaks up. Lifetime tributaries last until the suzerain (not the vassal) dies or becomes part of another realm. Permanent tributaries are similar but provide a lower level of tribute and only break away if either actor becomes part of a different realm. All tributaries can of course try to break free on their own.

Essentially, the only way to make Britain break away from the HRE is to take it over yourself, or ally with it and hope to be able to help it as and when it tries to break away.

 

[Vohen]

Alright, thanks.
Permanent tributaries seem rather broken then, as it is, France is pretty much deadlocked from the British.
I feel like it would be better for the permanent tributary to have a realm size ratio to overlord restriction, the fact that two huge and powerful empires can have this relationship is quite ridiculous imo.

But fine, this is an interesting scenario to play.