My friend accidently fainted a Spheal, will it come again sometime when the Island Scan feature is used?
Every time Island scan is used, a new Pokemon is "generated". The species of Pokemon depends on the location and the day of the week. You can find another Spheal if you use island scan on Monday while on Akala Island.
Hope I Helped!
Yes, it will. You can get an indefinite amount of each Island Scan Pokemon.