The problem is the illusion of personal identity. If Alice and Bob play quantum rolette, you're probably not going to be Alice in the universe where she wins or Bob in the universe where he wins. You'll probably end up being someone else altogether. One of them dying does increase the likelihood of being the other, but it goes from 1 in 6,000,000,000 to 1 in 5,999,999,999, not from 1 in 2 to 1 in 1. There's no reason why being Alice at time t has to have the same probability as being Alice at time t+1. They're two different people.