*WARNING: MAJOR SPOILERS FOR SEASON 8 (ESPECIALLY THE LAST 7 EPISODES)*
So in season 8, Meg returns and is killed by Crowley, adding to the laundry list of despicable things he did that season. (*sigh* And yet I love the character. Stupid awesome Mark Sheppard character with his charming personality and voice I've recently realized is ridiculously attractive... >_<) As part of the boys' trials to close off Hell (long story), they need to "cure a demon". They ultimately go with Crowley. (Oh ho, karma, thou art a wonderful thing.) They mostly succeed, but fail to complete the trial because Dean stops it so Sam won't die. Plus there's the whole: "Angels are falling from Heaven" situation...
Anyway, the Troper said they felt Meg was wasted in the end, and could have been used for the trial/redemption instead of Crowley. But I disagree. I think it was for the better the writers did what they did. For one reason:
Meg was kinda already redeemed by that point.
You see, over the last three seasons, she had expressed romantic interest in Castiel, and was working more with The Winchesters. She had kind of already swapped sides by her own vocation.Yeah, she never really expressed remorse for her more questionable actions earlier in the series, but she had gone good for the most part. Rather than being forced to do it by purified Sammy blood injections. If she had stayed alive and they used her, it would kinda have been pointless. Easier, but pointless. And if there's one thing I've learned from this show (heck, from fiction), is that writers can never have things be easy for their characters; there always has to be a struggle.
Secondly, and this is something a friend of mine brought up (regarding the revolving door Supernatural's afterlife), is that Meg's story was kinda done by "Goodbye, Stranger". She'd had her redemption arc of sorts, and I don't think there was/is much to do with her now. She's served her purpose. Yeah, I liked her interactions/chemistry/relationship with Castiel, especially in the last episode she was in (the scene where he patches her up is so sweet). But I liked The Winchesters' relationship with Bobby, and he had to die. (And I'm kinda alright with it.) I don't think that there would have been many story options with cured!Meg that couldn't conceivably been done with her character as it already was, or do much character development she hadn't already had. (Except maybe a "yeah, sorry about the whole: "trying to kill you multiple times, helping my father, kidnapping your dad, possessing Sam, helping Lucifer, etc. My bad, guys. I was TOTALLY in the wrong on that one...")
Now, Crowley, on the other hand, I think has more story options with a possible redemption arc. Like I said, he did a lot of despicable things, especially in Season Gr8. Seeing him dealing with guilt from that and seeking forgiveness from the boys could be interesting. Plus, since the ritual wasn't completed, will Crowley regress from "I deserve to be loved!" back to opposing our heroes? (I don't think that would've been an option with Meg.) Will he become a perment ally to the boys rather than one of convienence (especially with Abaddon running around)? And if he'd still maintain the personality the fans liked about him in the first place? If handled correctly, (and without too much "Draco In Leather Pants"-ing) I see a lot more ways a Cured!Crowley arc can go than a Cured!Meg one.
So anyway, those are my two bits. Yeah, it stinks Meg died, killing a link to the beginning and yet another female character. But I don't think it was entirely a waste. She was a good character by the end, but it was her time to go. She'd had her arc, her redemption, already. Now, it's Crowley's turn to have an arc.
(Besides, the stuff where Crowley finds his humanity is entertaining as heck. And Mark Sheppard freaking SANG! Missing that would've been a waste... ;P)