Not sure about that, every shit training school likes to keep a slightly dim witted, easily controlled, psychotic, sociopathic arsehole (that is most likely on the run from the authorities back home) on the books forever; it means that if all the other foreign teachers see sense and leave, there will also be the guaranteed presence of at least one dancing white monkey to keep the business going.

Therefore, you CAN teach English in China (almost) forever, but normal people wouldn't want to do that.