It is a scientific fact that energy cannot be destroyed. It can change state, for instance when heat is applied to water it converts into steam and if a cold temperature is applied it turns to ice.
Human Beings are a ‘form of thought energy’ that expresses itself through organic matter; the physical body.
When that physical body ceases to maintain life the ‘form of thought energy’ is released; known as death.

Death is merely a conversion of existence for the ‘form of thought energy’ that reverts back to its original state; known as Spirit.
Therefore upon death we do not cease to exist, instead we continue our life without a physical body, and in a totally different environment.
Just like water it does not cease to exist when it turns to steam or ice. It is fundamentally the same but just reacts differently in its new form and surrounding environment.