Freeman Dyson explored the heat death of the universe in "infinite in all Directions": https://www.amazon.com/Infinite-All-Directions-Lectures-April-November/dp/0060728892  In chapter 6, he used an operational definition of life, which is organized systems using entropy to do work, and evaluated whether life could continue to exist in the universe at various stages in the heat death process.  
His conclusion: life could exist at every stage of the universe he ran calculations on.  However, not HUMAN life.  He postulated that life could transform its fundamental substrate and matrix to other forms to continue to survive the universe's drop toward absolute zero.