How can the removal of the soul make the human body immortal?

[Erebus]

Preformationism is the study of organisms that develop from miniature versions of themselves. All human beings exist prior to their development as homunculi, taking the form of miniature humans within the nucleus of the male sperm cell. These sperm cells combine with female eggs, giving the homunculus a place to fully grow into an embryo. The soul is the last part of a human to be created, forming within the seventh month of the embryo's development. This soul functions as the consciousness of a human being, and is the immortal part of a human that survives after death. It acts as the software that controls the physical "hardware" of the mortal body.

By Replacing the biological process with an artificial incubator to complete fertilization, the soul is prevented from being created. This forces the homunculus to develop without a soul, leaving it an empty shell. These beings are technically "alive" but are not "conscious", lacking the self-awareness of a traditional human. These beings are treated as biological machines used for various purposes, such as war, service, etc. Their physical forms and be manipulated and aged in-vitro, leading to many different sizes and shapes.

These homunculi are biologically immortal, unlike normal humans born with souls. By removing the immortal software from the body and allowing it to develop without it, it makes the physical form unable to die naturally. How can this be explained?

 

[Prince of Spires]

If death is the removal of a soul from a body, then if there is no soul it can't be removed.