Adam Jahns, Chicago Blackhawks beat writer for the Chicago Sun Times says over Twitter that the Blackhawks have yet to be in contact with Hjalmarsson:
When I spoke with Kevin Epp, Hjalmarsson's agent, an hour ago, he was yet to hear from the #Blackhawks. He does expect to hear from them.
As noted, one can assume the team will eventually be in contact but it's interesting to note that no conversation has been had as of yet.