generally, for every day skipped eating, you lose about 1/2 lb. if you know your TDEE, you can find out how much fat you personally use up in that time, because an entire day skipped is just a 100% calorie deficit. everything else is water.
you can just subtract roughly 1/2 lb for each entire day fasted from total weight lost and it will give you a good idea of what to expect.
Half to all of it temporarily. Usually after losing around 5lbs my body swells and I gain like 2x the amount then lose it over a couple day period. So don’t stress if you regain a lot, just trust the overall process and take photos, compare against clothes, etc.