An ejaculate has hundreds of millions of the little buggers, but there can be only one winner. What happens to the also rans? Their corpses litter the woman’s vagina and uterus and fallopian tubes. Is there a mechanism to scavenge those organic molecules, or do they just mix with the fluid in there and become one with the woman?
Gravity.
As Genya Ravan once sang, “I won’t sleep in the wet spot no more.”
Yep. They just find their way back out the way they came in for the most part.
Certainly not all of them though. Right?
Well, since the alternative to coming back out would be staying in there and, as you say, “becoming one with the woman,” my question would be, wouldn’t she fill up over time?
No. A woman’s body will attack and destroy sperm cells as though they’re “furriners”. So the ones that don’t get expelled won’t last too long otherwise.
Cervical mucus is produced on a pretty constant basis and one of its functions is to work its way downward and expel any detritus.
I could have gone my whole life without hearing that phrase.
Can I go back to thinking of it as “girl honey” now? 
I am not saying she is going to fill up. I am asking whether there is a mechanism to break them down and enter the normal metabolism, or whether it is “everybody out of the vagina.” Is the mechanism solely immunological? Perhaps this cannot be answered with certainty.
Are you asking if they get digested?
I once saw a photo of sperm corpses in a woman’s Fallopian tubes and wondered the same thing. So I looked it up and yes, they eventually get broken down and absorbed into the woman’s body.
Once in my younger days I asked a girlfriend what happened to it and she said the same thing several posters here have: “Most of it goes down the commode”. 
The first thing you have to remember is that the unsuccessful swimmers die in relatively short order. At that point they are simply foreign matter. The body (male or female) dispatches foreign matter relatively efficiently.
What do you call a hooker with a runny nose?
Full.
Just FYI, I think “hundreds of millions” is … um … overshooting.
Actually, if Wiki can be believed (I haven’t got access to the citation), sperm number increases to an average of 240 million by two years from first ejaculation.
Thank you, Starving Artist
Ugh.
The vagina is an extremely inhospitable place for sperm. They have several things working against them from the start.
- The vagina is acidic for them (though it is more alkaline around ovulation).
- The vagina is the wrong temperature for them.
- There are bacteria in the vagina that eat them up.
All of this is balanced against the fact that they have to travel, against gravity, up to the uterus, which is why women trying to conceive are often told to lie there for some time after sex. Sperm don’t have a happy time in the vagina, and quite frankly, sometimes I think it’s pretty darn lucky one reaches there anyway. This is why you guys make gazillions - to increase the odds.
Sperm don’t last long in the woman’s body forever. I’ve heard estimates of up to seven days, but usually they guess less than 3 days.
This is all from my basic sex ed class waaaaaaaaay back when. What are they teaching kids these days? :brandishes walking stick:
Some might find that hard to swallow.
Just keep in mind that in the human body, millions of cells die every day and break down and the components are absorbed and used or discarded as waste products by surrounding cells or by cells whose job it is to police the area. Dead sperm cells are just more garbage to deal with.