The mind is just a byproduct of the brain. When the brain dies, the mind dies, so there is no "afterlife." The energy that sustains the brain is the same energy that sustains the body. This energy comes from the environment in form of food. Remove this food and the body will die, as a result of the Second Law of Thermodynamics. This Law also says that all things eventually will "die."
In essence, the Law of Conservation of Energy and Matter states that matter converts to energy and vice versa. When an organic body has died, its matter decomposes, releasing thereby energy. In this respect then, energy is conserved. But this process is irreversible, due the Law stated in the first paragraph -- in other words, you could not take this energy and recreate this body