I wouldn't go to China. If it was a country I'd like to live in, or even one I would be interested in being in for a couple of years I'd do it, but not China.
I would do what I could to get a sabbatical or still work for them if at all possible, but if not I'd look for different opportunities once I got there. Much easier in media than many other things.
I wouldn't put my children into mainstream school in China & putting them in an international school means they definitely will not become fluent. But in other countries I'd consider mainstream school as them becoming fluent in another language would be part of the draw for me.
I think if you don't dislike the idea of going to China, then it's a great opportunity, but plan carefully. Find out exactly where you'd be living in HZ (it's a huge area!) and what the expat community is like there and how commutable it is from there to SH. Find out what opportunities there are for the children to attend things to become fluent (more fun than strict, rote, learning).
Even more important than that, really think about your relationship with your DH. Don't even consider it, if it's not very strong & if you know he wouldn't do whatever it took to support you, even coming back, if you were really unhappy. Will he do his best to be home? To involve you with his work friends? To travel while you are there?