I have lived a lot of "hand-to-mouth" contracts and quoting Statsman because this has always been my feeling.
As been said before, they rewrite the contract, you don't agree and poof - you're done at the end of the existing contract. This termination could come early if there is a buy out clause.
The escape clause might not be clear but I've seen it appear under the 'handling of dispute' portion of the contract. Depending on how it was stated, I've always had this rewritten for a third-party mediator. The reason is some might say some lawyer junk in the hopes that you won't pay a jabillion dollars or have some lawyer get 20% of the recovery and you are essentially working for or walking away with a lower rate (if you win). A mediator is much cheaper and the company will have to abide by their decision (unless extra provisions are added). Another factor (again US here), is the mediators can often get away with using common law.
A big example here in the US is most companies get employees to sign a right to work contract that prohibits them from working for competitors or clients until a certain amount of time has passed since employment (generally 1 - 2 years). Most employees abide not knowing that it is nothing but a scare tactic so they won't jump ship when being lured with higher salaries that the employing company doesn't want to pay - the contract isn't worth jack but I had them put in the mediator piece as part of negotiation just to keep my options open but never had to use it.
-dK