Carolina really screwed themselves. Necas was their best player and transformed their team because of his elite skating and ability to carry the puck and make zone entries by himself. Early in the year they were scoring off the rush a good deal with Necas and not simply grinding it out on their forecheck. Instead they were turning over pucks between the blue lines and counter attacking.
That game is gone since they moved him and in Rantanten they have another heavy Finnish forecheck player and that isn't giving them the extra dimension they need to make a deep playoff run. He will walk to Free Agency and they will have gotten essentially nothing for their best player and sacrificed this season.
Assuming that Necas would have walked next year anyway and they knew this, could they have gotten a better return by holding their cards until now? Looking at the market, you would have to say yes. Or pony up to the bar and pay Necas and keep him.
Colorado has played their cards perfectly too. Necas instead of Rantanen is a big win for them at the moment and don't forget Drury who has given them center depth too. Having added Necas, Drury and now Nelson they can make a legit run at the cup.