I don't think the window is closed, as long as some prospects develop well. If even one of Steel, Jones, or Terry can make an impact next season, and one of Larsson, Wellinski, or Pettersson can become a solid bottom pairing guy, they'll be fine next year.
Getzlaf-Kesler-Henrique is still excellent center depth. Rakell and Silf are solid top 6 wingers, while Perry and Kase are 2nd/3rd line tweeners. They will be a playoff team next year. If they want to contend then they'll need prospects to make some jumps.
No need to rebuild. I think we get spoiled sometimes even with the terrible playoff losses. The Ducks have taken it to at least six in every series they've lost except for Dallas in 08 and Edmonton 06. They were bound to have a really shitty showing eventually. Think how many sweeps we have been on the right side of. Detroit. Minny. Colroado. Winnipeg. Calgary. It was just bound to happen eventually.
I don't think it's because they didn't care. I think that's a lazy excuse for fans. They looked like they cared and I believe everyone was busting their ass. The execution was just downright terrible, and on top of it they could not catch a f***ing break. But that's sports sometimes.
All I know is, as a Charger fan, I would kill to see my team in the playoffs. Don't take that shit for granted.