The Sky equipment is yours, its not owned by Sky (once you've fulfilled your initial 12 month contract). If you cancel Sky TV then the box becomes FTA (Free to Air) and you will see a similar EPG to that whilst on contract. You will be able to view FTA channels but NOT Free to View (FTV) which require an active Sky card and subscription but are free themselves. That's where a Sky Freesat card works (it costs about £25 and will be valid for many years). Only you can decide if you want the few additional FTV channels.

One possible minor problem is the EPG. If you keep your existing old Sky card in the box then it will continue to show you existing region. If you remove the old Sky card then the box will revert to it's default of 'London' region. Not much of a problem, just keep your old Sky card in the box!