Even though you'll probably not run across it all that often, keep in mind that dialogue that spans multiple paragraphs (same speaker) might not have matching open/close quotes. And that's intentional.
<p>"Blah, blah blah.</p>
<p>"Blah, blah, blahblahblah.</p>
<p>"Blahblah, blah, blah, blah, blahblahblah."</p>
Would be perfectly valid, typographically speaking, yet will likely cause any "hands-free" Find & Replace regex/script/routine (that's predicated on one-to-one matched open/close quotes) to barf pretty hard.