I had two V6 Boxes and received a main box and a mini as replacements.
With regards to losing your recordings. if you upgraded then obviously that is a downside so you should take that into account before deciding whether or not to upgrade.
Bear in mind that if your box breaks down and needs replacing, you will still lose your recordings. This is the same whether you are with Sky, BT or any other provider recordings cannot be transferred from one box to another.