No work permit...do it still have to leave in 24 hours?

18 hours ago, BritTim said:

The more I think about it, the more I think what you write is logical. However, I am still unsure you are right. Note that the conversion named the school. A visa issued outside Thailand does not do that. I still consider it possible that the permission to stay based on the conversion naming the school could be treated differently than the permission to stay based on the generic visa issued overseas. My sense, knowing Thailand, is that (whatever the rights or wrongs) for something this uncommon, it could come down to a random decision by a senior immigration official on the day with little you could do about it.

Although it's often referred to as a 'conversion' it is really just a new visa being applied for on the basis that the person qualifies for an extension of stay. In this case the justification is work and the application is supported by the school/employer. The same principle applies if applying at consular services.

Once the 90 day permit to stay has been issued there is no problem changing employers or not applying for the extension. Assuming the school/employer had provided a work permit, and the OP had quit, the school would have no influence over immigration to cancel the permit to stay as it is not a conditional of him working. The OP's problem is not with the school getting his permit cancelled because he quit his job, but with them informing immigration of his illegal work.