Without any proof to back that up, I'd say it remains a decision to the end. If there's people who can sit still while they are burning alive, I don't believe cannibalism is dependant on outer circumstance more than personal disposition.
I guess this is the kinda thing that would show what kind of person you are. Cannibalism may be a pure moral conflict, but then again one must ask themselves why they live at all. Et cetera - in a post-apocalyptic wasteland more than anything, your principles and integrity is all you have. That's why for example in the MM universe, those who've ever caved in and finally ate another human corpse are called "over the edge" - once you open certain doors, establish the nature of certain solutions as viable, you can never go back. It's not a thing you're doing, it's a complete trail of logic you are enabling for yourself. I am fully sharing this notion.
P.S.: The jerk thing to bring up, but food really isn't the problem in Fallout's Commonwealth, is it? Even if you cannot hunt, irradiated food in reality is not as (quite) fatal as it is often made out to be.