The final seating changes never happen at your desk. They happen in the venue office, in the car outside the printer's, on a train to the wedding - all places with terrible wifi. An offline chart is not a luxury; it is the actual workflow.
Not a cached web page that expires. A folder on your computer that contains the whole tool: open the file, it runs, no connection, no account, no analytics ping, nothing.
Offline is also the privacy answer. A tool that cannot reach the internet cannot upload your guest list, by construction. The list moves only when you move it - to a printer's USB stick, for example.
Save your chart as a .Print one test sheet of each PDF at 100% actual size before the batch. Charge the laptop. That is the whole checklist.