You are right. You will get an application-denied-7-days-to-leave-kingdom stamp when your extension application is denied.
BUT be sure you are still on the first 90 days immigration stamp (permitted to stay until), NOT the expiry of the work permit.
You also better cancel your work permit beforehand at the labor office.
You are going to go to the Chaengwattana Immigration office, Government Complex Building B to apply for an extension based on whatever reason to get 7 days stamp.
You will go here.
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And you can book online if you want to
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