The right of privacy of communication and correspondence is a right embodied in the Constitution. During illegal search, documents taken from you cannot be used against you and it is inadmissible in any courts in any proceedings.
With regards to written documents recovered by the relatives after the death of the patient (just a list of heartaches against the company he was previously connected, might be the caused of his sudden death), is not included or one of the exceptions. The right of privacy of communication and correspondence cannot be invoked by the company if such documents are vehemently manufactured. The company has no cause of action.
Much more if the deceased wrote it a minute ago before he suffered cardiac arrest.