With all due respect, I think that this is a somewhat different situation. I had a friend who was an exceptional metalworker commit suicide recently*, and his goodbye note also asked everyone to destroy his work. We have all kept his creations, not only out of selfishness, but also because we considered this request to be a result of his depression rather than a true wish.
Even if the person involved is of sound mind, I do draw a distinction between works of art, which are in many senses public material, and personal diaries, which are written with no audience in mind and may contain much that is nobody else’s business.
*Damn do I miss you D’ Drennan, you were a work of art in your own right