Sperm die within hours outside the male body when exposed to adverse abiotic conditions like air. The vagina is even more hostile to them through the abundance of lymphocytes which kill and consume stray sperm. Only those sperm cells going beyond the cervix survive... for up to 5 days. Most (80%+) die within 1 day. Fertilisation takes place within 48 hours anyway so the rest of the sperm just die out and are flushed out or consumed.
I just dug a little deeper and it is disputed here and there. And besides it just fucking freaks me out.
