thanks for the hint. Since i am using ASDK so i was able to find a function where we can set if the package will expire or not and how long is it valid.
for someone looking for the same problem, the exact function in API is:
SWDSolnAdvertisementManagementLib.SetAvailabilityRemovalOptions(sAdvertisementexGuid,
bRemoveAfterSuccessfulRun,sAvailableFrom,bExpires,sAvailableTo,bUseServertime)
Cheers,
fatima