If they never launched your app, your app never registered to Apple Push Notifications on their device, so you can't send them push notifications.
In addition, your server is not likely to have the device token for a device in which your app was never launched (since it's the app's job to send the device token to your server).
And if you push a notification to a device token of a device on which your app never registered to push notifications, the notification won't be delivered (even if the app is installed on the device), and that device token will eventually be returned to you in the feedback service.