They should give you a new card and box.
The old card will default to a free view card and the new one will contain all your viewing data (assuming you're
not going for multi room).
You can move your old Sky box to your holiday home permanently and take your old card with it. this will give you a load of free channels. You can also take your new card and put it in when you get there and you will get your normal 6 (or 2/4) mix channels but you wont get any premium channels (movies, sport, PPV) as these are only available with the card is in it's paired box.
I know this works as my old box is in the kitchen with a free view card so I can watch the news and stuff when cooking but if I want to watch something on Sky One for instance I need to borrow the card from my Sky+ box.
If you've gone for multi room then you're going to need to keep both boxes plugged into the same phone line as they phone home occasionally to tell sky where they are (they know from the CLI on the line) to stop you giving one to friends or family for a discount second subscription.
Sounds like you'll be able to do what you want though - just take the card and not the whole box.
Also just to mention - your sky+ won't tape anything while you've borrowed it's card (or if it does you'll not be able to play it back) so if you intend to tape stuff while you're away you'll need to leave the card.