I am not a Buddhist.
So here is something I know just fleetingly.
Nirvana is not death, in the sense of "born again".
It is not the death of the old self, birth of the new self.
It is a mental state (I think).
Our minds are in disarray, and impure.
It is possible to systematically purify the mind.
And attain the state of nirvana.
Which is actually the continuity of ourselves.
If you ponder, meditate, or quest deeply enough
And suddenly your muddled mind is clear, and you somehow
"know".
You have clarity of the innermost mind without being affected by
conceptual thoughts.You have attained the state of nirvana.
But you will still be you, except that you are now wiser, (I hope
so).