Bane

Detroit could hold on to Yzerman because they had a pipeline of new talent that kept them at the top of the league. Colorado had lots of sought after assets they could trade to bring in new talent, plus top prospects like Stastny and Duchene. Calgary has no legit top 6 prospects, and has to trade Iggy to bring in a proven young talent.

If you don't use your best chips (Iggy, Kipper, etc) to restock, then you're looking at a 7+ year rebuild.

Iggy is far and away the best player to mentor young prospects. If you are hungry for them you trade everything else - Regehr, Kipper, Jbo, Langkow, etc...