i think suggesting Gagner to be expendable is really saying he didn't develop the way you wanted so lets trade him.
I think the Oilers should have left him back in junior then the AHL to develop but thats my opinion.
Woulda coulda shoulda doesn't help. Tambellini can only influence the present and plan for the future. IMO Gagner is a skilled small center, if he played more in junior or AHL he is still a skilled small center. I like Gags, I just wish he was 4 or 5" taller and 50 lbs heavier. He is fully capable of putting 60-80 pts a year, I'd trade Hemsky or Penner first.