After ejaculation, that is, once the sperm enter the vagina, their lifespan is about 2 to 5 days on average. The most powerful ones will die along the journey, though. After fertilization, both the dead and live sperm that could not fertilize the egg will be eliminated by means of phagocytosis (i.e. the body's own system of neutralization and elimination of substances).
Suggested for you: Sperm’s Journey to the Egg – How Sperm Meets Egg with Pictures.