I've never come close to that situation. I've gone down on a wife as part of foreplay, of course. But that was obviously prior to any penetration. After I ejaculated insider her pussy, I yielded my place to her husband as they reconnected. The cunnilingus stage was over. However, the wife didn't mind resuming fellatio with either myself or her husband as play continued. Females can be less uptight about tasting bodily fluids during sex, I suppose.
The husband half-joked that the volume of semen I deposited inside his wife served as an excellent lube.
I have kissed girlfriends after my penis has been in their mouths. So, there's that. Can't say that it was my favorite thing to do.