Question

what happens to our DNA when we die?

Answer 1

It depends on the type of organism. The DNA is more stable in lower organisms such as bacterial cells as they can remain metabolically silenced for millions of years through the help of their spore forming ability.

Answer 2

When an organism dies it's DNA also dies. If the dead orgaism is preserved
under freezing condition or with chemical treatments, then it's DNA remain conserved for million of years.

Hope it helps you.