Well I'm not sure of the exact numbers relating to the timescale of the eventual re-collapse (due to gravity) of all the matter in the universe, but taking out of account the black holes taking matter into far reaches of space/hiding them/what ever they actually do/etc wouldn't matter slowly gravitating inwards and becoming more generally dense in respect to the space it consumes increase the heat transfers?
My point being that if black holes just "hide" matter by distorting light, and don't launch them into far reaches of space or other "bubbles" as Michio Kaku would say, then wouldn't the transfer of energy begin again (at least until all matter collapses back to a singularity/explodes again)?