I think they just endure it. If you look at past threads you'll see a lot of "I'm glad I didn't throw up" which implies the need to is over
I've seen this in a recent goodbye thread, posted on this forum a few weeks ago. It was
@CocoToxBase story;
https://sanctioned-suicide.net/threads/goodbye-thread-3.162754/ & 9 mins after drinking the SN she said;
"7:09 feeling little breathless
and a little bit nauseous but I can hold it back - still no pain
7:19 feelif very light headed and the room is spinning a bit, i can't sit up - still no pain my stomach feels fine
and the nausea is gone sats 86%"
The impression I got from reading the rest of their thread was their symptoms of nausea was strongest in the first 10 mins of drinking the SN. Once they got passed that 10 mins (doing very little to disrupt the nausea) that is when their burly vision other symptoms kicked in. Which ultimately led to them being on their way to ctb'ing until fate intervened.
Moral of story, if you can get through the first 10 mins of nausea or so without vomitting, then you MAY have absorbed enough SN? So after that point even if you vomit whilst unconscious, well depending on how much you might vomit, you might be ok? MAYBE.
As I cannot recall to many goodbye threads that failed after keeping down SN for longer than the first initial 10 mins. And I think
@CocoToxBase said she would have died if her dog hadn't rang the door bell.