My permit says ‘family member of an EU national’ not family reunification. I found a thread on here where someone asked about this on their c permit.
The feedback was that this legal wording in terms of saying how you received the permit, but didn’t mean that you lose it, If you are no longer a family member.
The feedback was they just change the wording on the c permit if your circumstances change, unlike with a b permit. At least this is how I read it.

Well..mine did. See the image - that was on my C Permit. I am non EU married to an EU National. I got my C Permit in 5 years instead of 10 years for Australians under the early C Permit rules "Vorzeitige Erteilung der Niederlassungsbewilligung".

I also applied myself and became Swiss. Just do that. Then divorce.

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Mine says the same.. I think my concern right now is more whether there is any issue with me moving elsewhere (same Gemeinde) and whether this impacts the c permit which has just been issued.

I presume from your post that the old codger has no idea you want out of the marriage? How do you suspect he will react when you spring the news on him? If you both want out and have no kids I would advise to play the game and just remain married until you get full citizenship. You can always move out and live in your own place and date/see other people without formally getting divorced. Once you have that red little book you can formalize things. You say you are financially independent so maybe you can come to some agreement with him to forego any alimony or financial support in exchange for remaining married long enough to get Swiss Citizenship.

I don't think it would impact the C permit, but do consider if you want to naturalize that municipalities and cantons have residency requirements as well - and you don't want to reset that clock.