I was really afraid of never for a long time, there was always something coming up that required my drinking. In the end, it was never worth it and it was never for just one event. I know that I never want to drink again. Life is just so much better without it. For me personally, it's easiest to just deal with today. I won't drink today. My stupid addiction brain can deal with that. Thinking beyond that panics me a bit.
And...if you were to stop today, you would feel much better on the 7th and would have a lot more energy on the hike. The first 5-10 days were miserable. I know you have a plan, but give it some thought. You can always reformulate. You don't need some fantastic farewell or to quit on an auspicious day. Just stop.
Regardless, we support you.