Stastny is a pending UFA. They never bring back good roster players at trade deadline. They bring back picks and prospects.
That's usually true, but if they do end up moving Stastny for the usual pick, prospect, roster player deal, the pick and prospect could be used in a separate deal for the defenseman they need, or to replace the pick/prospect they use in that deal.
In reference to the OP, I don't think the examples given necessarily relate to losing Stastny. They may be able to get by without Stastny because they have a lot of high end players already up front, but you're never better when you lose a Stamkos or a Quick, or Crosby/Malkin. Good teams can come together and put some wins together in the short term in their absence, but that doesn't mean they wouldn't suffer in the long term. That's what the Avs are facing with Stastny as a UFA.
I mean the Avs won the last two rounds of the playoffs and the Stanley Cup without the clearcut best player in the world at the time, Peter Forsberg, but they weren't a better team without him. They were just a well built all around team with three world class defenseman, Joe Sakic and some great forwards, and the best goalie of all time. The Avs aren't quite there yet. They would feel Stastny's loss for sure, but more in terms of his stabilizing factor, and his consistent two way play.
A big part of the reason for their success this year is they've finally got two lines going offensively at the same time for long stretches. They haven't had that in the past. It's either been Dutchy or Staz going by themselves while the other struggles. They'll need to replace his two way play up the middle in the offseason for sure, or slot O'Reilly back to center but he's been a huge part of Duchene's success this year on his wing, so there may be negative repercussions there as well.