Well, it kinda depends I guess. Did the agreement specifically state that he absolutely relinquished any and all rights to any portion of sacrificial meat at any point in time? If yes, and he knew this when choosing not to partake in the selection, then no, he shouldn't be allowed to eat, because that would be unfair to the people that risked their lives for the chance to eat knowing full well that they could be eaten themselves.
That being said, if not letting him eat is murder, then sacrificing someone to eat in general seems just as bad, as suicide is illegal as well, so even allowing other people to eat you would still be illegal, and I'm pretty sure that it would be just as easy to prosecute in court as for letting someone who refused to take the risk starve, especially when you consider that if they were, say, on a lifeboat or something of the like, they probably didn't have convenient access to a gun, so basically, they probably had to inhumanely tear him limb from limb and he probably died a very painful death, so there may be some torture charges applicable as well.
So basically, if there's the potential for prosecution either way, and I'm up for some cannibalism to survive, then I probably wouldn't be a big enough man to allow that guy to eat if he voluntarily chose not participate in the selection.