viewing another faction's power and deciding to go and raid them ICly because of how low it is is metagaming in itself.
Agreed. Instead, an RPC should scout the enemy faction's land, see if anybody who can defend it still lives there, then raid them. Remember - the things you do In-Game should be considered IC at almost all times. This loosely applies to building.
This brings me to whether or not Kappurfihgur's RPC should suffer for their actions.
The short answer: yes.
No, this doesn't mean you have to kill your RPC (but it's one of the most plausible outcomes of this and I beg that you do not ignore it). It means your RPC has been literally used as a punching bag by their friends to the point where it affected the security of the nation of Serenity, however that works. Certainly, that RPC must have sacrificed something for this and whatever you decide that sacrifice is, it must be made apparent.
In retrospect, I would have just left the faction, rather than stay in it and die 50 times.
My thoughts on Tyedye,
As for whether or not Serenity as a faction is able to persist:
King Redmond has no subjects and if no new faction members join soon enough, then realistically Serenity should fall. Redmond could then go through any number or type of character arcs: RPC death/RPC becomes a fallen king and stays that way/RPC becomes a fallen king and goes on a journey to become a noble and reclaim his kingdom/etc..
Just think about what your RPC would realistically think about or act in these situations. Also think about how you would feel if what you are going to do / have done were done to you. Make your decisions based on this.
If anybody needs or wants it, Staff can help you with your writing or roleplay. If you don't know what to do with your RPC, we can provide you with ideas for what happens next in your RPC's story/life.