How long do sperm hang around in the scrotum before being replaced or renewed? and what happens to the old sperm if unused?

Continually produced: About 1000 sperm are produced in seminiferous tubules of testicle from spermatogonium cells. Unknown how long they can survive in testis. Sperm trapped after vasectomy die after some time & are absorbed by body. Increasing length of time between ejaculation increases % of dead sperm in semen. Sperm can survive 5-7 days in woman's fallopian tube, but only few hrs in uterus. Die immediately in air.