A Sub-critical Density Universe approaches a constant speed at infinite time. Universe steadily cools down. Expansion continues forever. Next generation starts with a little less Hydrogen and more metals. Cycle of star birth, death, and birth is broken.
Nuclear fuel is exhausted.
Red dwarfs burn out as low-mass white dwarfs Remaining mass is locked into black dwarfs, cold neutron stars, and black holes. Wide binary systems are broken apart. Close binary stars coalesce into single remnants. Stellar remnants within galaxies interact over many many orbits. Others lose energy and sink towards the center.