Ehn was acquired mainly for the month where Raymond, Henriksson, Elmer and perhaps Niederbach is away for the WJC.
As far as I understand it, Ehn will not play any (or many) games until the WJC. instead he will focus on getting in to game-shape.
The major logjam comes after the WJC. Currently it's quite hard to get a spot on a team playing in Allsvenskan, they have a lot of NHL/AHL players playing there, waiting until the NA season starts. My guess is that one or both of Elmer and Niederbach will be loaned to an Allsvenskan team once the NHL/AHL players go to NA and a lot of roster spots opens up (which hopefully should happen sometime after WJC).