Typically, we'd expect a Call of Duty campaign to last around 7 hours. They've never been lengthy titles. The longest according to players on HowLongToBeat is Black Ops 3, the campaign of which should take players around 9 hours to finish.
Black Ops Cold War has three endings: a Good Ending, and two variations of a Bad Ending. These Endings will show once you've wrapped up all the missions in the game, and a short recap has played through that reiterates all the actions you've taken in the campaign to date.
