Mammoths had no appendix

I'm not aware that anyone has confirmed that in a frozen mammoth, but that's what I conclude from this article on the distribution of appendixes among mammalian species. Only platypuses, echidnas, some marsupials, most glires (rabbits and rodents), and most primates have them. None of the other mammals, including the order Proboscidea, have them. If anyone had a theory that the mammoths went extinct because of an epidemic of untreated appendicitis, you'll need to develop a new theory.