I believe in the next six months we could expect to see the 5DIIs go down a decent amount, but not huge. In the last week on eBay the range is $1500-$1800 on average for used versions. I am willing to guess that $1300-$1600 (depending on condition) will be the norm on the used market until the year end, especially given the fact many will end up upgrading as the year progresses, creating an over saturation of them on the used market. Outside of another major natural disaster in Japan, there is no way as others suggested that they will go up in value. It really does not happen with bodies like it does with glass given the technology. Also, Canon has a history of stating that the new version is "not a replacement, but will run beside the previous model. They said the same thing 60D, the 50D, 40D, 5DII, and on and on. They predecessor met it's demise within six months in most cases.
Outside of the last point, everything else is pure speculation on my part (like everyone else here) based on previous bodies pricing history.