Unless you can get an insanely large price, licensing seems to make more sense since you won't lose control of the app. You can relicense, including to those brick and mortar stores, and possibility hold out for a larger sum after initial success.

I would need to know more about your business to see how it fit your larger strategy, but turning internal tools into the core of the business has been a successful pivot point for others. The prime example the comes to mind is 37signals that went from a web-dev consultancy house to making productivity apps.