Will all of the gas in the universe be converted into red dwarf stars? Red dwarfs have lifespans of trillions of years and are also the most abundant stars, making up 70% of the stars in the Milky Way. No red dwarf star has ever died and none will die for a very, very long time. Because it take so long for them to die, they're not releasing their hydrogen back into the interstellar medium to make new stars.

As more massive stars live and die over the course of years, those stars release their hydrogen into the interstellar medium, which can form new stars, 70% of which will be red dwarfs. Does this mean that, billions of years into the future, all of the matter will get locked within red dwarfs until they begin dying out trillions of years later?
No. The reason is that gas recycling only recycles only about 40-50% of the gas in a sun-like star, leaving the rest as a white dwarf that slowly cools off. Heavier stars are even less effective in converting their gas into a condensed core. So the process will tend to produce a fair fraction of heavier white dwarfs now in the early stages of the stelliferous era, followed by a slow emergence of lighter white dwarfs from red dwarfs in the rest of the era.

Adams and Laughlin estimate that the final mass fractions will be brown dwarfs (never fused) 9.7%, white dwarfs 88%, and 2.4% neutron stars and black holes. In the post-stelliferous era some of the brown dwarfs will merge and make a few extra red dwarfs .