$100,000 a year doing basically nothing, and you sold it for basically nothing. They made the deal of the year, and you lost out big time. I applaud this guy for creating something popular, and monetizing it well. But that is up there with one of the worst self offs I've ever read. With only $500,000 now you're on the five year crunch to get a new product built or find a new job.
So rather than a chance that something may happen, you've guaranteed nothing will. The app could have just as well doubled its revenue. Selling out such an absolutely minimal work involved app is not worth the chance that the "economy collapses". Spend all that free time setting up apps on all platforms. You don't get anywhere without taking chances.
$500k is nothing to sneeze at. Some folks get too wrapped up in how important they THINK their business (or stock options, or whatever) should be worth or might be worth.
Rather than valuing them at what they're ACTUALLY worth.
It's not a risk that the economy collapses, it's a risk that his app isn't the #1 search result for Spanish language bible in the App Store. Given the nature of App Stores, he's one Apple search algorithm change away from making $0/month. Someone else could launch a free app that provides the same content and features and make his paid app irrelevant. Five years worth of revenue is a lot compared to that risk.
He also launched an Android version and it didn't blow up like the iOS version.