You think that they won't be jumping with joy if you approach them with an unpaid leave request off-season after what was an absolutely miserable season anyway? Having worked for leisure airlines most of my career, I have seen many people take a couple of months of unpaid leave in the winter to go and work on temporary contracts with other operators, fly someone's business jet, do a masters degree, spend extended periods of time with family abroad and whatnot else. In fact, in some ACMI carriers across Europe it's a company policy to assign everyone one or two months off work and off the payroll in the winter. Obviously, this may not be easy to negotiate if there's already a charter programme planned for the winter, but chances are that even if there is, it will not require anything close to the headcount needed in a normal summer.