I believe Lamichael's fantastic career for the ducks, being the 2nd best rusher in Pac history, and holding almost every rushing record for Oregon deserves for the number 21 to be retired. To me, he is the greatest duck of all time. Thoughts?
I prefer "legacy" numbers, instead. LaMike was known as a great teammate, a solid student, and a very hard worker. Give #21 to the player who best illustrates those traits, regardless of position. The University of Montana does it with #37 and has since the early '90s, and I know UW also does it for Curtis Williams' # (although I'd argue that his off-the-field troubles mar his on-field legacy to the point that the number shouldn't represent anything).
Even then, if they're convicted of a felony, repeatedly abuse their wife, and get arrested 5 out of 5 years at UW, and the only reason they died tragically is because the UW didn't kick them off years prior to the injury, I don't think a tragic death merits honoring that number.