If you send BTC to a custodial wallet (ie, one which you do not control the private keys for), then you no longer have control of your bitcoin (whoever has the private keys is now in control). If you send coins to a website (to buy some tokens, or whatever), then it is the website operators who now have control of your coins.
This is a well-known saying in bitcoin: not your keys, not your coins.
I would like to know, is there any way for those coins to be retrieved, or will they just disappear?
You can ask for the coins back, but if it is a scam, then chances are the scammers will not send you anything. You could report the scam/theft to local authorities, but chances are they will not be able to do much at all.
The coins will not 'disappear', they are just owned by the scammers now.
If you buy a token / cryptocurrency that is created and maintained by some central authority, then you are implicitly trusting that the central authority will not act maliciously. This is quite the opposite of Bitcoin, in which the user can trustlessly interact with the network, depending on no third party to receive/hold/send funds.