Offers are not permanent. They are tied to sponsor’s budgets and campaign goals. When budgets are spent and campaign goals change, your uncompleted offers may disappear.
The only way to ensure that an offer won’t disappear is to accept it and complete it.
Offers that have been accepted and verified will never disappear unless you take the posts down, change your Instagram handle, or switch your account to private before the 7 day pending period is over.