Small black holes decay measurably, but large black holes also decay, albeit at a much slower rate.Fascinating stuff but I believe that black holes don't decay.
The problem with this theory is that the expansion of the universe is stronger/faster than the pull of local gravity. Undoubtedly, galaxies will collide and black holes will eat up trillions of stars over the course of the universe, but it will not outpace the universe's expansion.Energy can neither be created nor be destroyed. So I believe that all visible matter will be consumed by the black holes and then they will combine to make the ultimate black hole, which will then explode in a big bang to create visible matter and smaller black holes that would create galaxies. So in a way no energy or information ever gets destroyed, it just changes forms.
Every period of the universe's history is full of black holes because black holes are the result of a collapsed / failed star.And since Scientists too have found that early universe was full of black holes, I think that this gives credibility to this theory.