Is it easy to cancel a Non-B visa and leave Thailand?

Very easy. Just leave the country and its automatically cancelled if you don’t have multiple entry 🤓

And are you on the initial 90 days of a non-B visa?

OR

Are you really on an "extension of stay" based on employment from the immigration office you got from being on a non-B visa?

Look at your stamp and see what it says.

If you're on the initial 90 days from a Non-B VISA you just leave and it 'cancels' when you stamp out

However if you're on an extension of stay from a Non-B, you cancel your work permit, get documentation from your employer stating you stop work on xxx date, you go to the immigration office cancel the extension and leave. You can buy a 7 day get out of thailand stamp after you've cancelled your extension for 1900baht <- (that gives you a week to get out) 🙂