The problem with them spraying the day before is that it will drive most of them out of their hiding places. They would have sprayed a natural or synthetic blend with Pyrethrin produced by chrysanthemum plants. It will drive the roaches crazy and they will come out and run around and end up dead in places they might not conceder. They should always inspect everything the day after they spray. You would have to ingest a very large amount to feel sick or have a long lasting effect. I doubt that the bug could carry that much on its body. http://pmep.cce.cornell.edu/profiles/extoxnet/pyrethrins-ziram/pyrethrins-ext.html I found a dirty mop string in my food at Applebees and will never go back. I understand your frustration and embarrassment caused by having a good customer with you during the unfortunate event. Good luck with what ever you decide.
Roaches are nearly impossible to get rid of in a restaurant. You can bomb and spray and bomb and spray but you're not going to get rid of them. I have family in the restaurant business and they own locations that are roach free but the ones that have roaches despite the amount of money they spend getting rid of them and the extra work of taking everything out of the restaurant and even replacing the equipment doesn't get rid of them....... At the end of the day it's just a bug, I would have problems going back there but there really is so much they can do as a business to get rid of them and occasionally they will pop up, no reason to bust their balls over it.
I'm sure you could get a lot more than one gift certificate. They should offer you at least twenty gift certificates and some candy from the general store.
Mitch- you seem to know a lot about bugs! On the drive you handed out some DEET spray that worked great - with 15% DEET.