The best of both worlds is to have a fake system—that is booted automatically, without any password etc. and with installed spyware—alongside your actual OS, encrypted and hidden.

You could even just keep data on your disk and have /boot on a pendrive (or a memory card, which seems more practical).

I'm pretty sure Hidden recommends that you create a guest account, so that the thief has an account to use.

I have a passwordless Guest account set up on both Windows and Linux for Predator. It's possible that as stories like this continue to get publicized thieves will get smarter and start removing or wiping disks, but it seems like a lot of the time they're not nearly that smart.