What if I deactivate the plugin. Does it return...

Absolutely ! Just deactivate it from admin panel and it will revert back. If you used ‘New WP-Admin Path’ make sure to remove or comment (//) related line in wp-config.php.

If you use a cache plugin you may need to flush it. If the plugin was deleted or renamed suddenly you need to visit Settings ->Permalink page (just visit nothing more!) and everything will revert back, too!

Since version 4, you can undo to previous saved settings whenever you want.