What is the process for canceling Non-B and Non-O visas in Thailand before departure?

Hi! I have a question about cancelling Non-B visa.

My wife works in the school, she has Non-B, I have Non-O as her husband. The visa and work permit are valid until May 20th (as the contract says), but the school year ends on March 29th and this is the day my wife stops working. We have a flight on April 4th, we want to spend last few days in Thailand travelling.

Is it true that we need to visit our immigration office within 24 hours of our flight to cancel our visas? It will be really challenging for us because of the distance. Can we cancel those visas on the airport? I’ve heard it is possible. We don’t plan to come back to Thailand anytime soon, even if we do, we will be using 30 days visa free entry. Is there any other solution which won’t be a total pain in the ass?