Doing a runner on a working visa is usually due to the teacher looking to avoid paying certain fines but having a working visa doesn't prevent you from doing the runner.

When an RP expires or is terminated there is the option to change it to an L visa usually for the period of 1 month. This gives teachers working on such a visa sufficient time to get things in order and if they want to find a new job they can do so. Equally (speaking from personal experience) some employers will not cancel your RP when you leave the school. Instead they will only cancel the FEC. This allows a teacher to stay in china until the end of the RP and find a new position without ever having to leave the country.

While there may be some short term benefits of working on non-working visas there are several problems that can develop in the medium to long term which could limit your flexibility. As one of the previous posters stated, there is a big difference between the interpretation of visa regulations by local authorities in china such as the PSB and the way a chinese consulate or embassy in a foreign country will view them. A previous colleague of mine recently had a problem when she went home for an extended period having been working on an L visa and then reapplied for a visa in her own country as she wished to return to China. The embassy refused her based on the fact that they felt she was using the L visa to work illegally in china (they were correct to assume this). Of course her passport was full of L visas which had been renewed over several years and it was quite difficult for her to deny the accusation. Perhaps you can share your experiences of how to deal with consulates and embassies in such cases.

I'd agree with your sentiments regarding working in china. There are no guarantees working here but there are things that a teacher can do to improve the odds of having a 'tolerable' experience as you put it.