Quote Originally Posted by TwinMfg
Generals age and die, and then are replaced with another general with very similar/same stats. This is probably what happened to you.

Once the new king has an heir, I believe his uncles stop being heirs (the silver crown will be missing from their portrait). They are still RKs, but not in line for the throne and will die off as above.
The crown will remain, until he dies of old age, it won't disappear immediately after he drops out of succession. Generals dying of old age only occurs in VI. It's purely cosmetic apart from that fact that you can marry a princess to the new general for another loyalty boost if needed.