I know this thread is 3 years old, but first one I found and it's a timeless subject anyway.
So, I was playing as queen of France and married my heir to the huge duchess of Toulouse, two years old at the time. ~20 years later, they have a son in her court, I'm concerned about my Jousting Lists because she is Frankish and I'm Occitain and the duchess revolts for independance against Burgundy (which controls only land in Aquitaine but considers that title to be more prestigious). She gets Pneumonia and dies. And my heir somehow inherits a barony in my lands. Next few years are spent whacking a lot of heretics and vikings and losing a crusade for Andalusia to a 40k doomstack, attrition and lack of allies (a few holy orders and 2-3 dukes participated besides me, that was it).
Shortly after becoming an Adult, my grandson dies, maybe even before my old queen died. Maybe shortly after. Sister (my daughter) inherits, who I had married to one of my dukes to prevent
him from marrying that duchess next door, I already was unable to keep Valois from inheriting Orleans earlier, much to my dismay. Dauphine has long been getting out of control by inheriting or getting inherited by random counties, too, but my king had a firm grip on his realm, so I was contemplating to just tyrany-revoke it... once this is over. What makes it worse is that duke isn't some 2 county loser, it's the duke of Burgundy. He already has a 6-county de-jure duchy and is on Primo. (at least the other guy has Gavelkind I refuse to go above MCA, so eventually it will break on its own)
Not wanting to risk that and I invite a duchy claimant who is Frankish, give him a county (Agen) and declare war on my daughter for his claim. While I'm sieging away, she dies of Pneumonia, boy inherits and I would now lose the duchy of Burgundy after the father's death. I declare again, and at 96% while carpet sieging, the claimant dies of poor health (no negative health traits) at age 41. His brother inherits, has a weak claim. Sufficient as there's a regency. I declare and actually win.
Now I have a > 40 holding duke with a wrong culture group within my realm. Obvious thing to do: plot to revoke! So again, I siege the hell out of Toulouse again and have 98% war score. "I still have untouched armies and holdings". I move over one siege stack to wipe the guy's last 250 men. I march to Armagnac, and the have nowhere to run. The duke is 41 - guess what? He got depressed and died, war ends inconclusively.
Third brother inherits. Also Frankish. I plot to revoke, entire realm supports me. I siege and siege and siege and he doesn't die on me.... instead,
I die a natural death at age 57. Dind't even realize I was already that old, king was 40 upon inheritance and did pretty much nothing else but working on Toulouse. And because my good and landed son had died earlier (he stayed Occitan all along btw, just doesn't help because he died) and I didn't have an old man face at the time so I wasn't concerned, I had remarried (Ultimo) and my heir was 4. War ends inconclusively, I'm 3 over my domain limit, 12 years regency awaits (at least my adult brother from earlier in that marriage is regent... for now. I should make him spymaster...) and the guy hates my new boy-king even more than everyone else does for being a bloody foreigner. And I lost 1000 gold worth of claims against what's left of K_Burgundy_in_Aquitaine what I had gotten in the meantime.
And I'm also going to have Auxerre inherited into Middle Francia for the second time, and can't do anything about it.