Not all Neutron stars will expand to the mass/density required to collapse into Black Holes. These ones will exude visible light for about one billion years before cooling down below visible light, then live on for about 1e+38 years before decaying completely into a kind of neutron white dwarf which will then decay further for another 1e+38 years before becoming a neutron black dwarf which will be there to witness the elder years of the universe.