I suspect that my father, if he were still alive, would also have no reaction to a letter that reflected on his alcoholism. No anger, just no real reaction. I might as well have written the letter in sanskrit.
Jeeze, I don't want to discourage anyone from writing such a letter. It is definitely good for the soul, cathartic, even if it is not well received, or received with a shrug and a 'yeah, uh huh, mumble'.