I have found when there are unresolved issues between two people when one passes away the issues remain for both people. Your father n law probably tried relentlessly to communicate with your husband, to no avail. I bet if you think back, you'll remember "strange" things happening or even an unsuall smell, anything that wasn't normal to you. It may have scared you and you choose to ignore it at the time.
How is your husband now that he has talked to his father (in the dream)? If you see that it has helped him a little, I'd invite dad n law back for another visit. : )
Libra