I did significant mil leave at another airline. Their AQP training system allowed an absence of at least two years (in my case) and think it can be up to three without requiring a full training event on return. It was a very minimal refresher, one day ground, couple sims and a checkride (LOE), and a little OE.

That might be your answer. If they're already paying the pilots and instructors anyway, and own or are otherwise obligated to the sim capacity, might as well use it now. When they get furloughed, they're a full-up 737 round, just need to wipe off the dust before sticking 'em in the breech when they return.

Otherwise they (well Uncle Sugar) pays bus pilots to sit around all summer, and then when they get recalled they'd have to pay them for months of training.

Obviously this only works well if the bid goes junior (bus vs. 73 at most airlines, that is how it works).