Given how easy it is to get a refund for an app purchase, I would be really surprised if this results in a significant revenue stream, but I don't actually know, of course.
Warren Buffett has a term for this, it's called "float". At my current (active, not abandoned) startup, my guess is somewhere around 30% of active paying customers are also non-users. Lots of industries have this. The majority of gym membership sales (50%+) and even a significant number of airline tickets are unused.