If someone hacks my Facebook account, is it that no matter what he does, can I always get back my account?
What is the maximum that he can and must do to ensure that I do not get my account back?
NOTE: Kindly take this Question positively.
You basically can always get it back. According to this article if a hacker has got into your account and changed all the contact info you still have the option to specify another e-mail address which the Facebook staff will contact you at regarding a password reset. If the hacker deletes your account and changes your password you must have your password reset and log in before 14 days time. This is because an account is permanently deleted after 14 days of no use (and the user requested deletion).