Simcha,
Now that I think about your question, I wonder if your premise is true. You make your premise on the idea that there is an issur of tarfus but there is no comparable issur for cannibalism.
However, now that I think about it, there *is* an issur on having hana’ah from a dead body. Generally speaking, issurei hana’ah are more stringent than issurei achilah. As such, you could make the case that you’re better off eating the tarfus (which is only an issur achilah) and not eating the dead human (which is an issur hana’ah).
Of course, when push comes to shove, both issurim get pushed aside for pikuach nefesh. But if you have a choice….
The Wolf (who, I guess, put himself back on the menu).