Users who don’t see that much value in your app simply leave. Among those who leave there are some who will be oblivious to any offer you launch at them. However, some portion of those users might be open to staying a bit more if you propose the right offer.
Since Apple makes available all the data to track those users including when they churn and how much time is left until they will actually stop being users, you can design different automated message campaigns linked to promotional offers to win them back. You will have ample time to act between when a user shows his/her intent to leave (the vast majority of users who sign up for a free trial cancel it on the same day) and (s)he actually leaves which means that you adjust the time of your offering. Add to that the variety of offerings you can propose, you can see that there is almost an infinite number of scenarios that could be tested against each other. Using Apple’s Promotional Offers along with automatic notifications (check Firebase, Leanplum and Clevertap) is the way to test constantly and find out the best Time/Price duo that is the most effective.
It is important to note that you will get 85% of the revenue after a subscriber accumulates one year of paid service (instead of 70% the first year). This means that you can offer up to 15% discounts to users that will complete their first year to keep them with no additional cost to you.