Pony Express:
You asked some great questions. I've been at the same regional airline for almost twenty years and I've been through two furloughs. I can't speak for the entire regional industry, but I can tell you what has happened at our company:
(1) We have a union, but the union's "involvement" in the furlough process is to represent the pilot group, make sure that management FOLLOWS our contract with regard to furloughs and downgrades, and communicate any news to our pilot group. We have never been able to put together a "furlough fund" to support our unemployed pilots. In fact, I'm not aware of any union (at the regional level) that has managed to do this.
(2) Concessions to avoid furloughs: In THEORY, this isn't a bad idea, but it's never worked in practice. Even trying to put a time limit on a concession is a risky strategy. Our union leaders know that. So I'm one of those "full pay to the last day" people.
During our most recent furlough in 2009-2011, we went from about 780 pilots on our seniority list to a low of about 560. About 15% of our pilots were furloughed, another 12% went out on leave, and a few retired or quit. The maximum "furlough duration" (for those unlucky souls on the bottom of the seniority list) was two years.
Hope this helps.