Recently, I discovered a very interesting thought experiment proposed by Hans Moravec in 1987. This thought experiment is called Quantum Suicide and it's basically a variation on Schrödinger's cat. Here it is: a man sits down in front of a gun pointed at his head. The gun is triggered by a machine that measures the spin of a quark. The spin of a quark can either be top-spin or bottom-spin and there's exactly a 50% chance of either measurement. If the machine measures top-spin, nothing happens with the gun. If the machine measures bottom-spin, then the gun goes off and kills the man.
Now, according to the Many Worlds Interpretation (MWI), each time the machine measures a quark, it causes the universe to split. One universe has a dead man and the other has a very nervous but alive man. If you repeat the experiment 10 times, you should have 9 dead men and 1 living man. If you repeat the experiment infinite times you will always have one universe where the man is still alive.
Next, throw away the quantum gun setup and imagine a more real world scenario where the chances of survival aren't as easy to measure. As long as the chances of survival are greater then zero, then at least one copy of the man will survive. Even if a nuclear bomb went off next to the man, there still may be some extremely unlikely, but technically possible event that saves the man. There should always be a tiny subset of universes where the man is still alive. Thus, every living thing is technically immortal.
I personally find this theory to be very comforting. It means that when I die, some version of me will always live on. I will never cease to be (at least until the universe ends but that's debatable whether that'll happen or not).