If a sick person needs to eat meat on Shabbos, or he will die, and the choice is between slaughtering an animal on Shabbos or eating neveilah, what should he do?
They should slaughter the meat for him. This is for a number of reasons. 1. We are allowed to do whatever the sick person needs. 2. The sick person will not want to eat non kosher meat. 3. There are opinions that it might be worse for the person to be over on many prohibitions from each piece of meat that he eats.
Ran End of Yoma that Neveila is worse here because it is a lav for each kzayis, O:CH 328-14, Graz 328-15, M:B ibid 39