You know best how he'd react but maybe you could get your Dad a nice card and express the concerns you've mentioned here, in a very respectful way.
In so many words, you could tell him that you love him and miss his presence in the house and that you've seen a change in him and in the family since he's become an Elder and it hasn't been for the better.
(Do a google search of "Ministers Kids" and get some statistics on how it effects their lives and maybe you know of some JW Elder's kids who've have had a rough time)
In a tactful way let him know what you've learned about the matter and how you already feel you are at the breaking point. Tell him you're afraid of the family breaking up. Tell him that you remember how the Society says fathers main responsibility is to put his family first and it feels like lately his Job and Congregation responsibilities are first and the family is suffering because of it.
Just an idea, but I know if my kids would have done something like that, I'd have definitely sat up and taken notice.