The box will work as if it is a retail box and will retain the functionality to be able to record, rewind etc.
You will lose any functionality associated with TalkTalk though. This includes access to their app, and any shows you may have purchased. You will also not be able to play back any recordings made from boost channels.
Your box will continue to receive updates as and when they are released by TalkTalk.
Hope this helps.
NB. When your contract ends the box normally becomes yours unless it has been replaced, when TalkTalk may ask for it back.