They had a 3 year window to win, and they won one, got to the 7th game of the finals once, and got to the 7th game against Orlando in the other year. They did what they set out to do, its over now.
Not that you can't go into next season with KG and Pierce but they're going to look a lot different next year. If Sheed retires it would help, Pierce could opt out and try to get one last big contract from the C's before the new CBA but I don't know how far they're willing to go.
Ask D-Wade how easy it is to rebuild. It'll be easier for Miami to do it if he leaves.
And don't forget that Perk is probably out until January.