Average length of a CPA offer?

Hey guys,

I'm curious on the amount of time a free trial CPA offer lasts before it expires? I have a campaign setup around one popular weight loss offer and it's generating some very good income. It would REALLY suck if it was to expire. So, to the veterans, realistically how long do free trial CPA offers last. I know it probably varies but any insite or trends you've noticed would be appreciated.

As long as the advertiser makes money - I think they will keep the offer running. If they aren't gaining profit, they will certainly stop running it. lol I'm not sure.