They cancel work permit you cancel non B … you have to return work permit to be cancelled… then you take letter confirming cancelation to immigration and they ( immigration ) cancel your non b … as long as your work permit is cancelled you can risk flying out if within a day of work permit cancellation
If you are going to don Muang you go to Bang sun station and change to red line …if to Suvarnabhumi ( more likely) go to Hua Lampang train station and get MRT linking to airport line