Subsister is a relatively uncommon word that simply means "to exist". There are a number of synonyms for subsister that can be used to add variety and nuance to your writing. Some alternatives include persist, endure, survive, live on, carry on, continue, and last. Each of these terms emphasizes a slightly different aspect of existence, such as resilience, longevity, or ongoing vitality. Other relevant synonyms might include sustain, maintain, or uphold, which imply a level of support or assistance that helps the object in question continue to exist or persist. Overall, there are many ways to express the idea of subsistence in your writing, and utilizing a range of synonyms can help you capture the nuances of different situations and contexts.