Eh, personally I would try it, but I've been known to do lots of things in my sleep. Such as kicking and tossing a lot.
When I first read this question I thought WTF, it's a physical impossibility.
Apart from the penis' shrinkage making it slip out everyone moves in their sleep which depends on the amount of time slept, however for eight hours it can be up to 200 times.
So anyway, WTF
Please consider a feasibility study before you ask the next question
When he's on top I don't want him to pull out straight away, I like to stay together for a couple of intimate minutes, but after that I wanna move around a bit, get comfy or clean up if necessary. A cuddle or sleep after some great sex is lovely, but I wouldn't want him inside me an entire night! That to me is just unnecessary hassle...
Keep it in, I love to fall asleep stuffed and satisfied
Ok..you have filled me with your cum. Now get the hell off me!
As for a cock staying in me, well, like the banks used to say about CDs, "Substantial penalty for early withdrawl"
"When its too kinky for everybody else, its just gettin' good for me."
(Kinky Freedman)