Oh yes, in case you are unclear about the Zaid visa (or Zee) it gets cancelled anyway when you get the 'Residence permit' stuck in your passport, and of course you use that to exit and enter the country as well as to give you the right to live here. Providing that when you fall out with an employer you scarper from their immediate area and don't offer yourself up to the police or other authorities,giving them the chance to put a line through it, then you are not a fugitive and have the right to live in China until said (pardon play on words) permit expires- It cannot very easily be cancelled, unless the company have the ear of really big guns in Central Government- Yuming would want to keep away from that lot. I am sure Yuming has other teachers who stay on L and F visas- now that's a different matter and very easy for them to cancel those. One of the reasons companies like to keep the expert certificate is that it's redeemable for 800 rmb in Tianjin, I am told (that could be nonsense as Chinese boss told me that) Another reason is that they use it to buy things in your name. And of course to make your transition to another company more difficult. I have always thought there could be another reason, just a power thing to keep you in tour place as 'white monkey'

Now, if I were in the position of being finished with a company with good time left on my R-permit, I'd just clear off- all the other companies know of Yumings track record and would not consider you as risky if they did employ you unofficially until you could acquire another Z and cleanly go through the process again at a later stage.