Yeah just leave a copy of your personal passport at the lobby for them to come back and pick up. Don't forget that immigration has scans and records of everything he submitted to them. They would have no need to randomly visit his hotel to get this information. If your friend is having doubts or worries he should visit the police station or immigration office to inform them what is happening.
How often I read about teachers pay being held over this and that reasons. I'm glad I never got involved with school's out here. Hope you find a good solution to this.
Similar to me. It really depends on your immigration office. Mine used to be fine with bringing the TM30 with my next 90 day report but when I came back 2 weeks ago they required it within 24 hours of arriving in Thailand. They informed me when I made my re-entry permit there to not forget to come in with it. It's really down to the property owner to go to them with it.