Crosby may be back by the last week of the season. If you drop him someone else may pick him up and affect the outcome of their playoffs, or yours if you make it far enough. If you hang on to him you may make yourself short handed. As long as you don't need another offensive player I think you should hang on to him so not to change the outcome of others playoffs.
But don't expect them to put him on the IR. They only do that when they need to clear a roster spot, and with the expanded rosters now they won't have to.