SKY engineer here, without a subscription your box will become effectively a freesat box.
Your current card will just have the subscription channels disabled on it ,so any free to view channels will be available still.
Also by keeping your current kind in you still be able to view Channel 5(not available when you remove the card) and also the regionalised programmes like BBC and ITV will be correct for your region still ie.Granada for the Nth West,Central for down south etc.
You may notice 1 or 2 channels that are not available that you would get on freeview or a Standalone Freesat box.
If you have had your Sky box for 12months or more it is now yours,Under 12 months and Sky may send a engineer for it.