I recently came back from about 5 months off after a wrist injury. I just spent the first couple of weeks working my way through all of the body parts, starting light and working up a little heavier, but nowhere close to where I was lifting before.
On the third week I started back to my regular routine, only not as heavy. I can tell a lot of difference in my strength and even more in my endurance, but after getting pumped a few times it doesn't seem like I've lost much in size. It sucks, but the only thing you can do is work your way back--it shouldn't take that long.