health.stackexchange.com would be better fit.
Your minimum healthy weight is not dependent on city versus outdoors. Your body is not aware the calorie deficit was caused by a hike.
The body is very good at storing and using fat. That is what body fat is designed to do.
I am not a Dr. but if you got home without severe symptoms you did not harm yourself. Symptoms of starvation include: diarrhea, anemia, loss of muscle mass. If you went into loss of muscle mass your body would have told you big time and you would have had a very hard time finishing.
Lose some body fat is the most efficient way to carry calories.
Even on a medical supervised extreme diets they go up to 1 lb a day.
Pro fighters move two weight classes and still perform. Look at Connor McGregor at 145 (where I think he still holds the belt). He fought Diaz at 168. Even training for a fight a pro can lose up to 1 lb a day and still train hard.
For a number you should see a Dr. The Internet cannot tell you that. Even a Dr. is going have a hard time with a number. They will be more interested in symptoms of starvation.