App uninstall tracking is prone to errors and for iOS/Android, no company can do it 100% accurate. Therefore, experienced analytics experts try to find customers before they uninstall, and reach out to re-engage with them, as they are aware that a user uninstalling the app cannot be easily reached out and we can tell that there is an end of lifecycle for that particular user.
Reaching out to users who are starting to "churn off" can be done using a few ways:
Use our slipping away users plugin to find out who haven't been using your app for more than 7, 14, 30, 60 days. For more information and screenshot, see https://count.ly/plugins/slipping-away-users/
Other method is to find out all users who haven't been active again for a number of days, using Drill functionality, and reach out to them via push notifications.
Hope that approach helps!