Well I think it has this monthly fee depending on your call/text/data plan right? if there is still money left in your sim card as it reduces every month, it will last forever.

You can go to an official service center and ask for a 停机保号(stop service but reserve your number). Then it will be only 5 yuan a month(5 yuan as last time I checked.). You will need to activate it once every 6 months.

the wife thinks it will stay active for 1year after the last time you use it with money on it

From personal experience - 1 month.

I left here for about 6 weeks, returned, and I couldn't use my phone. I was told by a girl at a small CM stand that you only get 30 days of non-use before it becomes useless.

However, never forget the old 'if you don't like one answer, just ask someone else' thing that goes on here.

I bought a sim card at Beijing airport, that allowed me to call to foreign countries as well. I put 200 yuan inside of it. And I did not use it for 7 months, came back to China and it still worked.

I can't remember the service provide though, some major one because the Beijing airport staff guided me to a machine and some person next to the machine helped me to buy the card from it.