How many truly dead stars (which are not dwarf, neutron or black holes) are there in the universe?

No, there hasn't been enough time yet. Unless you count white dwarfs, which I don't. White dwarfs have stopped producing energy by fusion, so they are just slowing radiating away their heat. But the oldest white dwarfs are still at a few thousand kelvins.

It will take at least 1 million billion years (10^15 years) for a white dwarf to cool down to 5 K.

Probably none as of yet because the Universe is not considered old enough. Also, they would never reach absolute zero.

Ask that in one of the other universes (in the multiverse) that's several hundred billion years old. Maybe someone there knows the number of them in that universe.

I've never heard of such a thing, the cores of stars don't dissipate the same way as the star's outer shell. The gravity has to turn the cores into something. The closest I know of to completely gone is a black dwarf which is a core which has cooled to essentially a cold black stone invisible against the backdrop of space (our sun's end fate) if you really want nothing, send in a black hole I'm certain it will be happy to finish up the job and gobble up the remains.

No, probably not. I do not know, and I don't think anyone else knows except obviously delusional people.

no there has not been enough time for black dwarfs to cool.

it takes trillion of years to form a black dwarf.

Twenty six

how would we know sweetcheeks