It sounds like you have no ties to a particular area and are financially sound to weather a downturn. JB isn't going to get any better than it is right now. UAL will offer way better long term opportunities especially at your age. I'd say go.

Regarding furloughs I think it would have to get really bad like another pandemic or WW3 bad for the airlines to furlough signifigant numbers. They're much more likely to offer early outs to seniors than to furlough and struggle again to get pilots on the other side. They remember the self induced pilot shortage well.