We want to remove our app from the App Store and shut down the servers that support it. From what I've read, removing the app from the App Store will not remove the app from the devices of the existing users - and there is no way to tell users to remove it.
Is there a standard way to tell the users that the app is no longer supported? Should I just send the users a message (in the "message-box" feature that our app has)? Should I upload a new version which opens a popup message telling the user that the app is no longer supported - and remove the app from the app store a week later? Will apple review accept such app update, or turn it down claiming that the app is unusable?
I'm less concerned about the specific mechanics of shutting down which is also discussed here, but I'm looking for customary procedure or examples of how this is done well.