*DISCLAIMER - not all of these guys are top 4 guys I'm strictly choosing teams who I believe could miss, and have guys available with less than 2 years on their deal.
My guess for defenders that will be on the market if these teams:
From Eastern Conference Teams:
Pittsburgh - Marcus Pettersson, Matt Grzelcyk
Columbus - Ivan Provorov, Eric Gudbranson?, Jack Johnson
Montreal - David Savard
Philadelphia - Eric Johnson
+ maybe
NYI - Mike Reilly
Detroit - Ben Chiarot, Jeff Petry, Olli Maatta
Ottawa - Travis Hamonic
Buffalo - Connor Clifton, Henri Jokiharju
From Western Conference Teams
Anaheim - Cam Fowler?? (unlikely), Brian Dumoulin, Urho Vaakanainen
Chicago - Connor Murphy??, Alec Martinez
Seattle - Jamie Oleksiak??, Josh Mahura, William Borgen
SJ - Cody Ceci, Jan Rutta,
+ maybe
Calgary - Rasmus Andersson?? (unlikely), Tyson Barrie
LA - Vladislav Gavrikov, Andreas Englund
Minnesota - Jacob Middleton, Zach Bogosian, John Merrill
St Louis - Nick Leddy, Ryan Suter
Utah - Ian Cole, Robert Bortuzzo