Highly intelligent people with excellent academic qualifications do not necessarily make the best teachers, in my opinion. Many of them are so brainy that they can not see the potential problems that their students will meet in what is being taught. Too clever by half to be a good teacher, one might say.
That said, I just thought it worth mentioning that that American had taught illegally at your university. Fact is, a Z visa is only permission to enter mainland China to teach, not actually to start doing so. You should not start teaching until your Residence Permit has been procured for you by your employer.Your well-qualified friend could have refused to teach until he was given his Residence Permit! Of course, that wouldn't have gone down well with his employer, but the law is the law! One could say your university pulled a fast one by not getting him an RP. That would mean his Z visa would revert back to an L, valid for 30 days from its date of issue, severely reducing any options he might have had due to time constraints!
It's about time that Chinese employers started following their own country's visa and work permit laws. They are bending them to their advantage, and contrary to that of their foreign employees!
To sum up, no teaching should be done till you've gotten your Residence Permit.
Visa type, L or F or Z, is irrelevant in that regard. But of course, you can't get an RP without first having a Z.
And Hong Kong replacing L's with Z's for mainland. Can't understand the logic behind that - it's got me stumped. What's wrong with provincial capitals doing it, as they used to do before? After all, they're part of China too!
As for your former colleague's air ticket home, I'd have thought the cost of that should have been reimbursed by the employer. But in China, there are too many unscrupulous and dishonest employers, even in the state sector!