A demo might sway some of the doubters out there, and the pre-alpha was both very stable and offered a great introduction to combat, which is after all 90% of the game. You could even post a sticky about it in the forums if you didn’t want to put it up front.
If they do, I’d suggest slightly updating it with the new look of the game. You want to give people the best possible impression of your game, so that you don’t miss out on people who aren’t convinced by some of the old placeholders. Maybe something to do just before the game is fully launched?
What exactly demo doesn’t have that the full version has? I am asking, because I’ve found it to be pretty accurate representation (I’ve bought the game already; partially convinced by YouTube videos, partially by checking out the demo).
Off the top of my head, the most noticeable is that the wïederganger looks different and is called a zombie. So it’s not that much right now, but I’m thinking more of what the game might look like by next year as development continues and the differences increase. At launch is when you want to draw people’s attention and when most people will try the demo to see if they like it.