I can only tell you what *I* would do, OK? I would stay PUT! How do you KNOW that, after quitting a Class I railroad, that the smaller shortline wouldn't experience reductions in business later?
Then what? Unlikely you can come back to UP. Remember: Often, the Class I railroads FEED traffic to these smaller roads! Sometimes the shortline is made up of the VERY trackage that the Class I abandoned.
I know it is tough, but furloughs are PART of earning one's "whiskers" in the industry. There's not ONE of us who traveled the same road 10-20-30 years ago that didn't go thru the same furloughs.
Again, it is up to YOU, but I would stick it out.