Unless you're an O6+ you won't be competitive, and even then, they may not be making currency exceptions four years from now.

You can 100% return to your old airline (assuming it's not shutdown and you are not in a furlough status below the recall line). That's probably the path of least resistance, go back, get current, build the time you need and basically pick up where you left off in your career.

You lose four years in aviation but gain mil pay and bennies plus retirement points.

I don't think majors will hold the mil time against you under the circumstances (although an equal candidate who slugged it out in the aviation trenches through the hard times might get preference if it came down to the wire).