Food allergies are no joke. With that being said, if a restaurant fails to make good on an order from a customer who specifically asks for certain problem ingredients to be left out, it could be viewed as fair for them to send the order back. As long as the sending of the order back is being handled in a fair, respectful matter it shouldn't be too big of a problem at all. So, this customer asked for a new burger, the restaurant refused, and then the customer decided to only leave enough money for their drink. Some folks in the comments section are in agreement that that was a reasonable move to make.