This is a continuation or confirmation of Do I need to turn in my old equipment?

I recently upgraded my Galaxy S7 Edge for a Galaxy S8+ just past the 12 month mark in my Edge "lease".  The website stated that, due to the remaining value of the S7 Edge, I could upgrade at the half-way point for free by returning my old phone.  When I received my new GS8+, it came with a helpful, handy padded envelope and UPS return label.  All's well.

EXCEPT, I now have Returner's Remorse.  I'd like to keep my old, working GS7 Edge as a backup.  What's the process for notifying Verizon Wireless that I'd like to keep my own phone?  Do I simply NOT return it and let them bill me?  Will that incur some penalty or early termination fee, or will I simply get a bill for the remaining ~10 months in my previous 24-month Edge lease?

¡Gracias!

- Dave