Edit:
As stated out in the comments, silent notifications aren't affected by the user permissions. The only thing you have to take care of is the notifications format:
The sending of a silent notification requires a special configuration of the notification’s payload. If your payload is not configured properly, the notification might be displayed to the user instead of being delivered to your app in the background. In your payload, make sure the following conditions are true:
- The payload’s
aps dictionary must include the content-available key with a value of 1.
- The payload’s
aps dictionary must not contain the alert, sound, or badge keys.
Source Apple
This was my old answer true for pre-iOS 8 versions (and still is for visible notifications, which aren't topic here):
If the user denies remote notifications, this door is closed. Technically you could think of your own background service, but this needs to run constantly in the background, e.g. via continuous GPS usage (bad idea).
A better option is to convince the user to accept and ask at the right moment in time. This article should give you a rough direction what to think about: http://techcrunch.com/2014/04/04/the-right-way-to-ask-users-for-ios-permissions/
