The only certainty is existence.
It is not death.
Death is a horizon. A event that changes state. A change of state does not nullify existence.
Saying that because I existed today and died tomorrow does not negate the fact of my existence nor does it negate the fact of my continued existence, albeit in a changed state.

Humans see things through the lense of perception but that presents false images.
What is, is. And always will be. Even at the death of the universe what was still is. It may have changed its state or configuration multiple times. Even nigh infinite times. But it still is. It still exists and will into eternity.

Only complete non-existence is the opposite of existence. The complete annihilation of existence.

And that does not exist in our reality.

I may be weird. But I find that completely comforting.