In the Many-worlds interpretation (MWI), when we say that “a + b” collapses to “a”, there is a shift of definition of “you”.
MWI is in one sense correct: choice b version of you still exists. But the trick is that he is not in another universe. He is in the environment of this universe.
And perhaps in reverse, you are also part of the environment of him.
2012.02.22 Wednesday (c) All rights reserved by ACHK