It is the same person but a different human. Even if they drift apart, by all means, their own personal identity is the same, same as if we split the universe with 1 human taking path 1 and in another universe the human taking path 2.

The moment they change, they are not the same person, just as I am not the same person I was when I started writing this reply, and yet, I still am "me", irrespective of the drift.