No, in watching the playoffs, the winning teams have not relied on the top lines (anymore than normal). It has been and continues to be those "unproven" third liners like Gurianov, Kirivanta etc. along with 2nd line scorers brought in, like Pavelski.
When ours (Dube etc.) were scoring we had a chance to win the series, when they went cold - we were done.
3 wins away from the Stanley Cup, I know I am not in awe of Dallas, I'm sure many are not. I don't find their goalie to be all-world and my only observation is that they have 3 lines that can score, giving them a chance to win nightly.
So, if the new second line is Backlund, Tchachuk and Eat Bread and the 3rd line is Bennett, Looch and Dube - that's fine, but they need to score key goals 5v5 vs. other playoff teams.