You don't lose stats at all. You have 2 accounts once you buy ViP, your Non ViP account(original account) and your ViP account(FB server). You can either choose to transfer stats or not to your ViP account. But once you transferred, you can't transfer it back to your Non ViP. Most players who bought subscription usually transfer their accounts because it's easier to stick with one account.
To transfer accounts, just open the main menu once you bought the subscription. Then click on "VIP Account" & check to see if the email is right. After that, press login and then a screen will show up, asking if you want to transfer your stats/furniture/items. Check the first option, then it'd log you into your ViP account with all your items. If you want to go back to non ViP, then just re-log and click "Don't use ViP Account" in the bottom left corner of your screen.