This would not happen. Every single time I used bitcoin as a payment method, I was presented with an invoice payable in btc amount that has a timer. As long as your bitcoin transfer (transaction) is in the mempool, the sale contract is complete. If your invoice timer expires before you actually send the bitcoin, don't bother sending, the sale is voided.
This problem I never had with any fiat money.
Last friday BTC was over 40K and 72 hours later it was around 30K. if you buy groceries it is not a problem as you pay instantly, so the volatility is not a huge problem. Althought it can fall or go up 1K in minutes. But if I want to sell a house ( or sell a car, boat or plane) I need several days to prepare all legal documents. A drop of 25% is than dramatic. Or I lose the money if I persist in the sale, or I lose the sale. With fiat money I never have that problem. I know that in 1 month my money will still have the same value.
Same problem with savings. If I need some money from my savings urgently and it is a bad moment I can lose up to 80% of the value of my savings (biggest drawdowns). I don't have this problem with fiat money. Savings is related to safe; but your savings are not safe at all in BTC as you never know what the value will be when you need it.
Why would I take such a huge risk?