You have the full authority to automatically convert crypto deposits into fiat if that's what you want. It's okay for me as long as you can sustain those withdrawals in crypto but there might be some issue on your end if the price goes up. I think that will be the issue for your customers who really like withdrawing in crypto if it will also be affected if ever your system upgrades. But, if you can simply put that feature of letting your customers to decide if they would like to convert it to fiat, I think it's the best.