You should change the offer when the offer ends. There is no guarantee that you will get a commission on that link. Commissions could of been disabled on that one affiliate link by the owner of that business.
This question to get a straight answer is to email each website and ask this question. Only staff can give you the right answer.
I don't leave up ads that the expiration date has passed. It makes visitors think I don't update my blog often or care about the small details as in update ads.