They can currently join existing kingdoms (like successful rebel clans).
The player cannot persuade them currently as the defection persuasion assumes a kingdom to betray - that is to say that there is simply no content (dialogues, decision making logic) for this context. We are considering a content addition for this, but I cannot say if and when it will come.
what
@Totalgarbage said.... Before when we "destroyed" kingdoms, they existed pestering us but eventually clans would scatter.
I like the new possibility to destroy kingdoms, man... but the rebel clans/independent should
A) create a new or restore their faction
B) become mercenaries (and eventually the possibility to be recruited as full clan by any other kingdom, AI or Player
C) be "indepent" for a time until declre the pledge for other faction or allow player to bring them in specially since they don't own lands
Please, don't return that silliness of exile because of the lack of other places for them to exile too