[mothered]

DNA is an option, but it's a heavy item (8kg)

The weight has no relevance to the DNA method.

Whether It weighs 8kg or 800kg, It doesn't change the fact that you're purely claiming It didn't arrive, Irrespective of how heavy It Is.

and has tracking that will show it's delivered.

GPS/tracking Is a useless form of verification.

It only confirms delivery to an "address", and cannot conclude a "person-to-person" delivery. As such, you did not personally receive your goods.

DHL will probably take a picture of me with the product.

"Probably" suggests Inconclusiveness.

Try and establish whether or not It Is the case.

Would DNA still work in this case?

It depends on the circumstances of my comment just above pertaining to receipt of goods.

Their terms say if the product is not as described (damaged, etc) I can ask to return it at the expense of the seller

How do you plan to circumvent the return?

But I don't know if it's that easy to "prove" it's damaged.

You will be Instructed to provide the evidence.