If my memory serves me correctly Wally was fired once before and hired back as a contractor because people outside the company appear smarter. I can't remember how that ended but I'm sure if you have the time to go onto google you'll find it.
You can't fire Wally - its the thing you can not do. (Or has it already happened in the past? Must have been a continuation strip, until he is back in his original position.)
Shrink his empire? He has a better chance of shrinking his cauliflower size hemorrhoids! It couldn't be any smaller unless he fired Wally and transferred his salary to Dilbert's project (whereupon Dilbert hires Wally as contract labor for the project - voila! - continuity).