I am not aware of any post with my tags.
If you have tested the app, once you have made a subscription or purchase, you will get email with a bill.
When the subscription is about to expire, I think Google will send email to notify the user about the end of subscription.
You don't need to personally tell your users. However a friendly email reminder can also be done if you have their info but some users may not like to receive too much redundant email notifications.
Example 1,
I think subscription base is more suitable if you provide online services with continuous usage or download of products such as songs, videos, comics, articles or tutorials. So the app should connect to the Internet.
Example 2,
I would let the library handles the access.
I don't have any real app with subscription right now but the above are just my opinions.