I have had client lock themselves out all the time. So if you are the only person who has access to wp-admin and you lock yourself out, then you are screwed. I have done this myself because I couldn't remember which password I used. I deleted the plugin ... took some more guesses and got it. Then re-installed the plugin back.

I have blocked my wp-admin and wp-login.php by IP address, so no outsider can see that. on top of that, there is limit login attempt.