Assuming proton does not decay, then via quantum tunneling, a white/black dwarf will transform into a giant lump of Fe-56. This would put the last object to exist or even be able to exist forever an iron ball, outliving even the largest of black holes. Just a fun possible fact.
Meh, black dwarfs are speculation. Containing iron is hardly mysterious, though I am interested in the weird phases of matter it may have till then. I would also hypothesize that proton decay isn't out of the question, it's simply our inability to observe such events that leaves us without the evidence to support such hypotheses.
The fate of the universe is absolute harmony. No entropy or enthalpy as literally everything, and thus the absence of everything, is squeezed to equidistance, equiradiance, and equigradience.
