The most accepted number on attrition is about 25 - 30 pilots a month...usually. So you can assume in the span of a year they will lose 300 to 360 pilots. So eventually, yes, they will have to start hiring if they intend to keep airplanes in the air!!! They can't go on forever without new people coming in.
See, I'm not all negative and doom and gloom about the hiring potential!