Answer to both theist and to reductionist.

You’re talking about the eternal life of the “self” or “soul”, the eternal life of your personality – which is a nonsense when there is no proof of any such entity: not even in your conscious life now.
What is one’s “self”? Is it your brain, your nerves, your other organs, your blood, your skin, your eyes, your limbs, etc? Are any of these your self?
No. Self is the name you give to the consciousness of your existence. But this consciousness is itself just the functioning of your body, of the matter you consist of. Consciousness is an effect of matter in motion. Consciousness is a quality of matter itself, and the type of consciousness a being has is typified by that being’s material organisation, and also that being’s society.
There is no entity “self.” “Self” is merely a convention, one of many terms we use in order to socially function.
From the time we are conceived and begin to develop in the womb, we are part of a material metamorphosis (with a species-specific society becoming an integral part of that metamorphosis from the time we are born) entailing reproduction and death.
That being said, matter is indestructible and (motion being as much a property of matter as are thought and feeling) the metamorphosis does not end with death. Life and death are integral to the eternal metamorphosis of matter.
There can be no non-material entities inside of us operating the controls, just as there can be no non-material author of the universe – simply because non-material implies non-entity, and only matter can move matter.