You are right, it will only affects him if he will going to withdraw it. But as long as it is still in his wallet, there's no problem on it. In terms of the figures, if he has an asset in bitcoin it will be the same but the value will change. Most of the gambler I knew are using doge instead of btc,but it's all depends on the gambler if he really needs to convert it to usdt or fiat.
The relation of it will depend on how much he has bought that bitcoin on his account. If it's during the high and he's got stuck there with 1 bitcoin, it matters a lot to that gambler. He can withdraw it and still get 1 bitcoin but the current price of it matters because it's no longer the same as high as it was during his purchase. That's the actual matter of it but if a gambler uses most of the time altcoins, then there's also the same relation on it but there is the feeling on how easier it is to gamble with those.