I found that your Stick and Rudder skills are like riding a bike. Once you can pole a 150 around the skys like a complete loon, you may get rusty but you never forget how to. Thats why many ex-instructor airline types like to do the odd day here and there, just to keep their hand in.
You take more with you into the airlines from instructing. There seems little you learn in the airlines that can be applied back to instructing though. IMHO of course.