Can't remember which one but credit cards were offline for a time with something and places that still had the carbon paper roller things stashed away took them out and used them. They should keep those things around.
Not sure how much good that'll be... A lot of banks are giving out cards where the numbers are only printed, I haven't had one with raised numbers in years.
Shop I worked for in 2005… I think … ran cards when the connection was down and took card impressions, and I think the transactions were all auto submitted when the connection came back up.