Xipoli Continent Elven Law Volume 41. If those on the edge of death were to become Devotees, they would be granted an entirely new body. But if their eggs were returned or due to any other reason they were turned back into men, they would be returned to their near-death state.
2. If the female body is also on the edge of death, the exchange of eggs will not allow them to recover. As the egg merely grants an additional body, if both bodies are severely wounded then they are basically beyond saving.
3. Illnesses that affects one body will affect the other, and although exchanging eggs may cure some diseases, there's also a high degree of risk involved.
4. Both bodies share the same lifespan granted by the Goddess Xipoli, so exchanging your egg will not extend one's life. However, other symptoms of age will not affect the other body.