Theoretically if a thread is locked, it can be unlocked. Usually when a thread is legit (not spam or trolling) it will be locked in cases of heightened tempers (case in point, the PPR forum which I avoid like the plague). If the flame war participants cool off after that, it is within a mods power to unlock said thread.
Although I have noticed in recent cases the mods have gone straight to the more drastic step of deleting a thread out of existence without so much as a nod to the people who posted. While I'm sure that they are trying their best to keep the rampant troll problem under wraps, it's still annoying when you're trying to re-visit a certain thread and you can't find it. The other day I was looking for the name of a WP member to add to my list of people to meet in RL, but the thread that I remember him in was deleted in this manner. Normally I'd have something to say about this kind of Orwellian data control, but the mods have already told me to shut my trap when certain words are concerned, so any accurate description I could think of would be a no-no.
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"Yeah, so this one time, I tried playing poker with tarot cards... got a full house, and about four people died." ~ Unknown comedian
Happy New Year from WP's resident fortune-teller! May the cards be ever in your favor.