Here is a coin that was holed hundreds of years ago. I liked it so I bought it. It will do as a "hole filler" until I want to spend over 1000.00 on one that is intact. William I (The conquerer)
The coin looks like it is in a holder that fastens at the top. So, the coin might not be damaged at all.
My experience with mounted coins is such that I would be very careful about their authenticity. In my earlier days I purchased several which turned out not to be what they were supposed to be. Once a coin has been mounted it becomes somewhat difficult to determine its age. If one has a coin from one's own collection and is certain of its authenticity and wishes to have it mounted as a keepsake or for a gift that can be a good idea. I have done that. Also keep in mind that there are mounts that the coin can be inserted into without damage to it. There are also what are called jeweler's cast coins, made from lost wax imaging, and made by jewelers solely for the purpose of mounting. After 50 years or so no one can determine where they came from or when they were made. At a recent coin show a dealer was selling gold ducats, holed at the same spot. They were from India where they were made as late as the last century to be worn as wedding jewelry. As the dealer was both knowledgeable and honest, this information was clearly displayed along side the coins. They were, of course, copies of genuine coins and their appearance by itself was somewhat odd. As to what the purity of the gold was, it seemed more like 18 or even 14 carat and not coin gold. Bottom line. Coin jewelry can be very attractive, and wearing something used by people 2,000 years ago has a certain cachet difficult to duplicate. But, be careful about what it is, not so much its esthetic appearance as its genuine antiquity.
Mexico has areas where it is still a tradition to offer a gold coin ( many are not really gold, but it is the thought ~right) as an engagement agreement to the father of the agreeable lady.
I rather like coin jewelry - mostly because you can find scarce coins at a bargain price, but also because they can be interesting. Here is a sample of stuff I've accumulated over the years: I have been fooled by fakes. Below is a Gordian III "sestertius" that is a modern cast fake - it looked pretty good in the auction photos, but in hand it was clearly a pot-metal fake: