Especially now that independent distribution of books and apps through things like the Kindle Marketplace and the Apple App Store isn't just possible but is also lucrative for many creators, getting your products back can increase your backlist and income.
It's not super-important to worry about reversion clauses in a non-exclusive deal. After all, if you can sell your creations in multiple channels then it's hardly a problem to be in as many as possible. But where anyone locks you into an exclusive deal then you may want to make sure you can get your rights back if they aren't actively trying to make you money with them.
And although every publisher has different reversion clauses, there are a few standard elements that you need to consider.
- The time period. Most publishers require that there has been no meaningful activity with respect to your book for a period of time. I've seen 5-7 year periods being standard, but maybe you could get less.
- The triggering event. Look for language like the book being "out of print" or "commercially unavailable". You'll want to make sure those terms are defined pretty carefully so that the publisher can't find a copy being sold second-hand in a flea market in Mexico and claim that means the book is still active. For apps it's a bit easier because reselling them is usually prohibited by your EULA (you did put that clause in there, right?) and so at least outside of Europe sales will usually only be in a controlled environment.
- What role do e-books play? If your publisher can release an e-book version and use that to claim the book is "commercially available" you can basically assume you'll never get the rights back. If at all possible, put a minimum number of copies sold or minimum revenue number in the clause so that one copy sold doesn't keep your rights from reverting.