I think KG will last till about 35, 36..then you will see a major decline. why that long? well, he takes good care of his body and is not only athletic but mad skilled.
Why? His biggest weakness is his lack of strength, and thats the last thing to go. When KG starts losing his quickness he will decline fairly rapidly, he already seems a step slower from the knee injury he played through last year. I guess the closest thing to him for me is Webber and has fallen off ridiculously quickly.
As for the trade... if Cupcake turned down any offer from Minny that didnt involve Kobe he should be shot. He has already butchered a title contender, if he didnt take KG for the entire damn team outside of Kobe he is stupider than even I thought possible and I rate him at the same level as Isiah. If LA can get KG, they do it. Bynum looks solid but you give up someone who is young and looks solid(Curry looked solid also, Kandiman looked solid) for a legit superstar.