When you stop paying a subscription to Sky, your Sky+ box looses all functionality as a recording device. You can't record programmes on it and you can't view programmes that you've already recorded. You can, however, continue to use it to receive all of the 'free to air' channels, which are listed here:
http://en.wikipedia.org/wiki/List_of_free-to-air_channels_at_28%C2%B0E#Channel_sections
A basic Freesat receiver doesn't really add much to that but many boxes now have 'on demand' apps and/or a recording facility:
http://www.freesat.co.uk/channels
You should note that, although the total number of Freesat channels is greater than that for Freeview, some of the most popular channels aren't available without subscription via a satellite dish. In particular, the UKTV channels (such as Dave, Yesterday, Drama, etc) are only available free-of-charge on Freeview:
http://www.freeview.co.uk/whats-on/channels