Bypass.

Out of the ~1400 original UA furloughees over 600 are currently flying at sCAL. The ones that wanted (or needed) to quickly return are already back at UCH. sUAL has officially sent out 342 recall letters and every single furloughee was offered a sCAL job last year and can go to sCAL anytime with a single phone call as long as classes are running. They haven't.

Considering that historically only around 50% ever return that means there's probably only a couple hundred still out there that will eventually return.

Of course, the big variable here is the SLI itself and where they end up. IMHO, with a positive result for the furloughees we'll see more of them sooner and if the entire group is stapled we'll see far fewer ever return.
The ones sitting out are sitting out because they can. The SLI will determine what they eventually do but with a 10-year bypass they have time to sit and watch and keep UAL in their back pocket.