Hawks didn't get their ***** handed to them by Nashville because of a lack of depth or core players regressing (though Seabs yearly decline is scary).
The reason the Hawks lost that series, in such devestating and embarrassing fashion, is because of coaching.
A few weeks prior to the start of playoffs, Peter Laviolette shifted his team's system. He gave the green light for his defensemen to skate through the neutral zone, instead of the more conservative way in which the system requires always having two men back.
Quite simply, Nashville, knowing that they wouldn't get anywhere with how they were playing, adapted. And with that adaptation, they got better at transitioning the puck up ice. The four teams who made it to the conference finals all played this structure.
Q didn't adapt. Our system is primary one that relies on the stretch pass, and the players on this team do NOT like to dump and chase. So when Nashville clogged up the neutral zone, our entire structure collapsed.
The one player who is good at skating through the neutral zone and up ice is Kempny. Kempny only got into the series after the Hawks faced the deepest of playoff holes. And Oduya, the guy who should've sat for Kempny, still got playing time in that 4th game (we iced 7 defensemen).
If Q can adapt, the Hawks can survive (at least for now). Otherwise, we'll do well enough in the regular season and go out with a whimper in the playoffs.