No, medals are there forever.
Once you have it, it can only upgrade.
You can even unfan a club you have a medal in, you will lose that medal, but if you fan that club again you get that medal back after some time. (I know this because I tested it myself)
You can't lose a medal just because you're not as active as you used to be.
The most you'll lose is a spot on the Top Current Contributions.
