A good chunk of those who left aren't coming back. My gut says anywhere from 1/3 to 1/4. That all depends though on how fast the conflict resolves. The longer the wat goes on, the more refugees will establish new lives in the West and have less incentives to go back. To be cynical, a large amount of young people may benefit from the war, as it allowed them to immigrate easily to far wealthier countries with greater opportunities in the West.