There have been previous accounts of people waking up after a failed attempt, although the reasons for this are still not quite known for sure. Read this thread of a couple of people sharing their experience:
https://sanctioned-suicide.net/thre...proper-medical-treatment.142737/#post-2254027
Honestly, while the odds of you not waking up are significantly higher if the regimen is followed properly, there's no 100% guarantee with this method. This is why SN while being quite popular here due to accessibility reasons, is not considered the gold standard which N was.
I'm genuinely worried about this a lot because if I fail an attempt and have to be rushed to the hospital, the cat's out of the bag. That's the last thing I want. I've been trying to source methylene blue instead and preparing a couple of syringes beforehand, in case I do wake up so I can self-administer it, but that's still a gamble. With situations like this, it's probably best if you get proper medical attention to minimize as much risk as possible of permanent damage but that comes with a steep price.