As we all know, the Kingdoms here live in lifecycles as much as any King or Lord to spare some time for their heir - be them competent or not. However, it would be rather unceremonious for such kingdoms to be put into the tomb without a proper rites behind it, don't you think?
With such in mind, I'm personally finding it an interesting suggestion to add Event for falling Kingdoms that would compliment their demise - one that is befit a King. The "End Game" Event which may involve relative to the plot events that have been recorded crucially destructive for the entire Kingdom and could've unfolded more fatal to every Lord of the Westeros with all the Game of Thrones. Be it the song of Ice and Fire, the High-Sparrows rearmed fanatics, or mayhap even a simple debt being a bit too high for all lands to pay out for the Iron Bank.
I know it may be a bit of an idea too upscaled to fathom for introduction, but I believe there is a chance for at least reinterpretation or discussion for alternative use of such scenarios to implement on. Be it the prolonged idleness of a Lord, or an entire Allegiance with Lieges and Bannermen.
