You could also simply switch to other crypto gambling sites that charge lower or zero withdrawal fees like Bitcasino, Stake etc because majority of the gamblers prefer withdrawing BTC instead of other altcoins.
Why? Because it's easier to convert to their native FIAT currencies through sites like LocalBitcoins etc when compared to altcoins -> FIAT.
I did not imply that anyone has to switch to other gambling sites. I implied that they can prepare for times when transaction fees are expensive on BTC, ETH network. I meant they have to prepare a few altcoins for their deposits to gambling sites and plans for withdrawals.
Some gambling sites only allow to withdraw the coin you deposit. Some gambling sites have marketplace or exchanges in their sites. You can swap between coins.