@Vince: Sorry. I guess I did not catch that it was his father. So, let us look at your specific question:
“I had a specific question about the issue of a dying parent being placed on or removed from life support; Does it count as an anantariya kamma if
1) a person chooses not to place a dying parent on life support or
2) if the person chooses to cease giving life support to a dying parent?”
First of all, in cases like this, children SHOULD NOT get involved in the decision making; it is far too dangerous for them. It is best to leave such decisions to the medical personnel (and maybe to other close relatives, who would not be subjected to anantariya kamma).
With that out of the way, I think either decision above could be counted as anantariya kamma in some cases and possibly not in other cases (as you said, it depends on what types of cetasika arise in the mind of the decision maker).
This is why it is best to leave the decision to others. Even if they make the “wrong decision”, it will not become an anantariya kamma for them. I remember a desana by Waharaka Thero, where he said that usually son-in-law or daughter-in-law could consult with medical personnel to make such decisions. That makes sense to me.