I think it would already become a mistake if a stock trader who accepts bitcoin for payments stores their funds bitcoin Instead of converting it to stable coins like USDT once received the payment.
It's only advised to let your funds be on bitcoin if you're ready to be a hodler which means you're alternatively diversifying your source of income to bitcoin and then you can always take your profits to promote your stocks.
Aside this hedging I don't think of any possible strategy to recover the lost unless you're ready to shutdown your stocks shop and focuses to hold on bitcoin investment and hodl untill you regain your losses.
He should also understand the extent to which customers are willing to accept bitcoin payments because forcing bitcoin payments should not make his business worse. Not all places people choose to pay for things with bitcoin and it would be very dangerous if he forced people to use bitcoin and should have offered the option as a convenience measure for his customers. Many people prefer bitcoin as an investment asset rather than using it as a means of transaction like fiat in general.
The reason is because of the habit of everyday use which makes people a little worried about this method. This is different if this is the case in El Salvador because it does not have an official currency like most countries so implementing bitcoin as a means of purchasing would be much more easily accepted.