Complex sentence: Ultimately, the film's debut at the Montreal World Film Festival in August 2008, which was rewarded with the festival's grand prize, provided the necessary incentive for distributors to select "Departures"; it finally received its domestic Japanese release on 13 September 2008.
Split into simpler sentences: Ultimately, the film debuted at the Montreal World Film Festival in August 2008 and was rewarded with the festival's grand prize. This provided the necessary incentive for distributors to select "Departures", which finally received its domestic Japanese release on 13 September 2008.