This rumor is CONFIRMED.
In episode 5.04 (The End) the original script says:
But instead, we become this. The only thing I think we have left, Dean and me, is each other.
If Dean says it’s time to go out in a blaze of glory, win or lose, so be it. I’m in. But then…
(smiles easily at Dean)
That’s just how I roll.
This script (which can be seen here) was won by Laura (tumblr user hidefan) in an auction at Rising Con in 2010. She posted it on her tumblr after having the script signed by Misha Collins at the same convention the following year. (x)
In the episode, Castiel says:
Except I used to belong to a much better club. And now I’m powerless. I’m hapless, I’m hopeless. I mean, why the hell not bury myself in women and decadence, right? It’s the end, baby. That’s what decadence is for. Why not bang a few gongs before the lights go out? But then that’s, that’s just how I roll.
(From Supernatural Wiki’s Transcript)
Therefore, the line was changed between the original script and the final version in the show, and this rumor is Confirmed.
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