like most of the other threads on this topic states, GS didnt accept the deal last minute.

Whether thats true or not, who knows.

Barnes is killing it in the playoffs. Did we miss out or did we never have a chance for that trade to happen?

Once GSW had Barnes the trade wasn't happening.

I thought there were reports are that the Nets preferred Wallace to Pierce and choose to trade for him instead. The pick the Blazers used on Lillard would have been the opportunity for the C's to get Barnes. Obviously there would have been no ECF run last year and everything would have changed with that.

The Warriors would probably still be playing if they pulled the trigger on the Barnes and salary dump (Biedrins or Jefferson) for Pierce. They might have gotten to the Finals, or won it all if LBJ tweaked a hammy. 

The reason a team doesn't do a young for old deal like this is if the young player becomes a star.  The reason a young team does a deal like this is that the team desperately needs a seasoned vet to close out playoff games.  The other reason GS makes the deal is because they're not going to be able to pay Curry, Thompson and Barnes if all of them blow up into all star quality players. The PP deal would have given GS two years of championship contention, and then if Pierce liked it there, could have signed a cap friendly deal to play out his final year or to as a 7th man.  The deal would have been revenue neutral for this year and next, since the have to pay the useless Biedrins anyways.

It would have been a win win for both teams, with Boston starting the rebuilding and the Warriors possibly winning a title. Yes there's a danger that GS is giving up a long time future all star, but some times that's the price of a championship.  Pierce would have been perfect for that team in the playoffs, as a sharpshooting, scoring wing that can run half court offense, rebound, and defend.       

How many first round picks would you be willing to send to GS to make it happen?