Chael should not retire. He is the unfortunate recipient of bad timing, just like Rich Franklin, and basically anyone else that was in their prime in the MW division while Anderson Silva was reigning. WIth Silva surely close to retirement in a few years (no way he's doing all 10 fights on new contract), that will leave the MW division wide open so if Chael can stick around for another year or so, he has a legitimate shot (as does Franklin, Bisping and all other top tier MW's) at the title again.
Same goes for Rashad and the other top tier LHW's. If/when Jones move up to HW, that opens up the LHW division in the same way I mentioned for all the MW's. I for one would like to see this happen to free up the logjam at each weigh class. As much as I like to see dominating performances by great athletes such as Silva and Jones, I think it's better for the sport and entertainment to free up the divisions and see who comes out on top!