Postseason rosters are going to look a little different if the NHL restarts.
In typical seasons, most available NHL-contracted players from a team's AHL affiliate and even some from juniors, college, or Europe will join their NHL club for its postseason run as Black Aces after their own respective seasons are over. There is no roster limit or salary cap in the postseason, so teams usually carry a large number of players.
For the 2020 playoffs, postseason rosters are expected to be limited to 28 total forwards and defensemen, due to the need to regularly test all players involved and likely accommodate them in hub cities.