Aircraft approaches are issued every 90 days. To stay up to date you need to have a book of these 'plates' for every region of the U.S, or a subscription to a service that sends you paper updates. If this happened in flight they would either get ATC to read them the plate, or check with ATC that whatever outdated plate they had was still accurate.

Obviously though this is a pretty big technical error on the part of Jeppeson (the app provider). It's pretty clear that it shouldn't be possible for the apps to stop working due to something done remotely. There is another provider, called ForeFlight, which I think does a better job, and I was glad to see they weren't involved.