THe thing is, you would make or terra form more habitable locations. Death is not an essential. Thanos was wrong.Just because the universe is expanding does not mean that more habitable planets and suns are going to appear out of nowhere. All that means in practical terms, is that distances between suns and galaxies will continue to grow. If no one dies, a world will be overwhelmed pretty quickly, and not just because of people having babies. Imagine hordes of mice, rats, flies, mosquitoes, all no longer able to die. All those animals laying hundreds of eggs in a go because only a few survive, are now all surviving. Plants no longer die and continue to grow forever. (We actually see this in-game to an extent, with the Botani and the Overgrowth in Alternate-Nagrand.) You age and age as your body shrivels and twists as the cells continue to fail to reproduce accurately.
Depending on the rules, it could mean things like cancers and tumours can't be destroyed either, as those cancer cells can no longer die, as well as everyone being in a constant state of starvation as the plant or animal cells can't 'die', and be broken down to digest.