It is possible to survive SN only if not enough makes it into your blood.
So if you don't vomit then no, it would be close to impossible to survive that much.
Even if you vomit before with 25g many people still die if they didn't vomit immediately but like ~10 minutes in because their body already absorbed enough.
Generally, 25g isn't necessary for most people, less than half will usually do the trick, but when you ctb you don't want to rely on "a high chance" you want to make it 100%, that's why 25g.
If you do vomit while being unconscious you're most likely still going to die for two reasons.
1. You might simply suffocate on your vomit.
2. By the time you lose consciousness ~10 - 20 minutes in your body has already absorbed enough, if you do end up throwing up after already being unconscious you'll most likely still die from what's in your system already.
Consider that people generally die from lower dosages as well, the big difference being that lower dosages take longer to kill you and longer for you to fall unconscious, meaning a longer time to deal with the - not exactly painful, but uncomfortable - side effects.
Meaning if you fall unconscious quickly you already have taken in more SN than people that fall unconscious late (~40m - 1h) and still die from it.
tldr How reliable is it? - essentially as reliable as a chemical method can get
