title: Is possible to check if the user/device still has my app installed?
body: <p>I'm creating a Flutter+Firebase app for a dental franchise. </p>
  
  <p>Every client will be asked to install the app before the treatment starts. When the treatment finishes, the system will send a notification to the device that will trigger a survey within the app, just to check the client overall satisfaction.</p>
  
  <p>The problem is, <strong>if the client doesn't has the app installed anymore</strong>, it must not send any notification, because the client will be asked to answer the survey before leaving the clinic.</p>
  
  <p>I thought about using <em>Firebase Data Messaging</em> to return an "OK" to the server, like a "PING-PONG" request, but it works only when the app is on background or foreground, not if it is terminated. </p>
  
  <p>There's any other method to <strong>confirm if my app is still active/alive</strong>?</p>