If the App has been removed from the App Switcher, iOS will not awake your app, since the user specifically asked for closing your app.
If the user open your app at least once, and do not remove it from App Switcher, iOS will awake your app
What we have done server-side to handle this is :
If the user's app doesn't connect in the minute after we sent the silent notification, (you can set it as you wish), we send another non-silent push notification to alert the user.
Since the App (is not closed by the user) should automatically fetch data, it should take under a minute.
But for that of course you need a more complex server code than simply sending silent push.
EDIT : (Getting a vote up on this question showed me that it was outdated)
This answer is no longer True... you can now with PushKit wake up your app to do some minor things (like downloading small chunks of data to update content) even if the App has been removed from App Switcher.
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