I wrote:"Furthermore, you'd have great difficulty getting through airport customs if you decide to exit the country EARLY without sorting out your Z visa first, as your residence permit would still be in date."
Generally speaking, teachers are not issued with multi-entry Z visas in China. So if such a teacher tries to leave EARLY, he runs the risk of being questioned at the 'port of exit' as to why, and possibly detained; especially if the employer has reported without much delay that that teacher has done a bunk, thus breaking his teaching contact without paying the fine stipulated in it.
I'd have thought readers would have understood that leaving EARLY meant leaving well before the expiry date of the RP could lead to problems on attempted exit unless the RP is accompanied with documentation from the educational institution allowing that teacher to leave EARLY on grounds such as mutual agreement to cancel the teaching contract. But I was wrong, sorry for that.
In any case, walking out on your contracted job is DECEITFUL, especially so, as there is a clause in Chinese teaching contracts that expects either party to MEDIATE with the other in cases of dissatisfaction or disputes.
I did also say that it would be UNWISE to leave secretly. Anyone with a vestige of common sense would be able to appreciate roughly why that would be so, in any case.
From now on, YOU,if you like, can give us all advice on what to do if we happen to feel trapped and depressed in our contracted teaching jobs. I for one would welcome some, just in case I end up working for the likes of Shane some time in the future.

To leave before your contract is up would not be wise. You'd probably miss out on at least two weeks' salary, not to mention travel allowance money for the Spring Festival holiday and/or air fare reimbursement (or part payment). Furthermore, you'd have great difficulty getting through airport customs if you decide to exit the country early without sorting out your Z visa first, as your residence permit would still be in date.
My advice, first fix up a new job. Then 'negotiate' terminating your present contract by mutual agreement.That would be the sticky part as you'll probably lose some of the money they owe you.
But of course, you can always do something as a last resort that will lead to you being fired - an extreme course of action indeed!
It all depends if you can get fixed up elsewhere, preferably in the warmer South, difficult right now as it's well into the 1st semester. But there are some ads for 'winter camp' teaching.That would tie you over until the new semester begins, provided you can get a new residence permit and another new job before then.
I don't envy your plight. You have my sympathy. Good luck.
Unfortunately it's too easy to get hired by ropey schools and colleges - there are loads of them here in China.