Just my 2 cents, but it's a no-brainer to finish 20. I'm a fellow Herk driver 8 years AD, 15 Res, retired 5 years ago. The steady check and even more important, THE MEDICAL, will make the unreliable airline industry less nerve racking. They can furlough much faster than they can hire.
It was mentioned several times already, and I concur, you need 6 years in the Guard/Reserve to retire, and it'll be exceedingly difficult to pull off the sanctuary deal.
Good luck.