Where is the boundary between our immortality and mortality?

We will be around forever. Not "us" as in "you" and "i" as we are right now but instead those physical and energetic qualities that go into making us. So in essence our composition -matter and energy and information exchange - is more or less eternal (conservation laws). We are immortal the only thing that changes is our configuration/ order/structure and with that likely our awareness/consciousness/ form/ state of being etc.

But we are mortal in the sense of our current identity as a person having a lifespan that ends. So where is the boundary between that part of us which never dies and that which does? If our mind is a (meta)physical phenomenon of the universe then where do we put the limit that says "this is what will disappear when we die" and all of this will stay. How do we connect matter "body" and "mind" if they are both natural to the universe and what does it mean to "forget" or "not remember" in the possible circumstances whereby we are aware and alive multiple times through the ecological cycles of nature?