Depends comletely on the company and their requirements at the time?
For instance my company offered unpaid leave, which we could bid for and was allocated in order of seniority and you kept your seniority.
Not surprisingly there weren't many takers!!!!!
As I had said depends completely on the company and their requirements wont be a problem at the moment in most airlines. But who knows what it will be like in 2yrs if there's any airlines left that is??????????