What happens if someone cannot attend their ED visa extension appointment on the last day?

At least in Bangkok (at all the immigration offices here) IF you have a queue ticket you WILL be served that day.. (they stop giving out queue numbers at 3:30)

So I'd say if he has a queue number he'll get his extension..

Also let them know there is no reason to wait until the last day your current extension comes up to apply for another one on an ED visa 🙁

They ADD the extension to the current stamp expiration date.

He could have gone up to a MONTH before his current expiration and applied for this extension.