App for Instagram Videos/Stories download
You would need to get permission from Instagram for it not to be removed, you might also have copyright issues.

5.2.1:


  Don’t use protected third party material such as trademarks, copyrighted works, or patented ideas in your app without permission.


5.2.2:


  Third Party Sites/Services: If your app uses, accesses, monetizes access to, or displays content from a third party service, ensure that you are specifically permitted to do so under the service’s terms of use. Authorization must be provided upon request.