We already know what happens. Our bodies decompose into base materials which are potentially used by the environment. We become spread out and become part of all life, or maybe in millions of years we'll be oil like the dinosaurs.
The soul is just human hubris. If you believe in evolution then there is no reason to think we evolved a soul at some point just because reasons. If we have a soul then that means everything alive has a soul. Which maybe the case, idk and then you're getting into some philosophical ideas like everything is a manifestation of the whole (Bohm) or there is a higher plane of forms (Plato), etc.
The soul is just human hubris. If you believe in evolution then there is no reason to think we evolved a soul at some point just because reasons. If we have a soul then that means everything alive has a soul. Which maybe the case, idk and then you're getting into some philosophical ideas like everything is a manifestation of the whole (Bohm) or there is a higher plane of forms (Plato), etc.