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You have unknowingly died many times already. Whenever you die, reality splits off and your consciousness merges with your body in an alternate dimension where you're still alive without you even being aware of it.
In the old reality you left behind, your friends and family have mourned you, while everything is perfectly fine in this one and you go on as if nothing ever happened. This continues on repeatedly.
Every possible way of you dying has or will have happened. The longer time goes on, the less chances you have at survival, yet you remain blissfully unaware.
People you know that have died have simply split off from the reality you were inhabiting and continued on in their own. In that reality, they're still with you, neither being aware they died. It's possible that their reality could one day cross paths with yours again.
Now here's where we get to the immortality part. It's possible to keep on living, but how that actually happens could be any number of factors.
Maybe you dimension hop into a reality where science advances so far that medical immortality is possible. Maybe in another one, rogue nano machine "grey-goo" takes over the planet and makes everyone immortal by accident. Maybe elsewhere by some crazy twist of improbability, a literal magic fountain of youth is found in the jungle somewhere.
There are many different paths that we could take. One possibility is where we all get our act together and create the future we want.