It is more interesting to know for how long and how much the price is going down. Just saying that it will go down (or up for that matter) actually amounts to nothing once the movement has begun.
Optimistic scenario:
https://bitcointalk.org/index.php?topic=467191.msg8068282#msg8068282Under a pessimistic scenario, the odds of which is less than 50%, it could go to $400-450 where there is a strong support. If it goes that low, it will take longer to rise to the old ATH, probably by the end of 2015 only.