If you fire your trainer and you stay below $0, you can't buy a new one. You're stuck with level 1. You're not properly training then.
If you're down to firing staff (and not high level... just level 4 trainer, level 1 pr, level 2 or 3 doctor) as the make or break moment for debt, you have bigger problems than your staff.
If you remember me, then I don't care if everyone else forgets.