iOS 8 and 9 users will receive the notification. They will be able to read the notification's text and the title (if one was included) but they will not be able to see the rich content or the subtitle (if one was included)
iOS 10 users running a version of the app that doesn't support rich push will be able to see the notification's text, the title, and the subtitle, but they will not be able to see the rich content.
For more information on sending rich push campaigns, see our User Guide docs.