Virtually all of the failed cases appear to be where people were found or called an ambulance themselves, or where the protocol (Stan's guide) was not followed very closely.
If you take good precautions to not be found, and have a certain amount of determination to undergo some discomfort without calling an ambulance, then the chance of success should be very high. Some members have vomited, but still been successful. In the cases where people vomited it doesn't appear they drank any more SN, yet they still appeared to succeed, although the recommendation is to have a couple of extra glasses ready, and to drink more in the event of vomiting.