The main advantage that having an auth gives you is that in order for them to hack your account they still need the code. Each code is only good for 1 login so when they get the first code (You have 1 sorry that was wrong message) they an either
1. Change your password
2. Login to your WoW account

If you then try and login again and have a new authenticator code you will again get an error message, now thats 2 in a row and if that doesnt set off alarm bells then you need to have your head checked. But with that 2nd code they can take the authenticator off your account AND change your password.

But you are still sitting at your computer and they (Hopefully) dont have access to your E-mail address. If your E-Mail logs in automatically or if you use a program like outlook/thunderbird for E-mail then you can simply run through the password recovery option with Blizzard the reset your password and put the authenticator back on your account.
Then its a simple case of logging into WoW on another computer (If you dont have one in your house call someone you trust and have them do it over the phone) doing this will mean that you disconnect anyone still logged into your account (IE the hackers) and they cant get back in due to the authenticator being back on your account.

So in effect if you have a small idea of what you are doing they will get at most 5 minutes on your account. They can do a fair bit in that time but nowhere near as much as they used to be able to when they login when your in bed and they have hours to strip you and the guild bank :P