I don't know how it is for everyone, but this is how it worked for my DH back in 2005.
My DH had heard rumors about it first. Then about a week later, he found out for sure about his furlough through a press release. Then, a few days later, he got some company memo about it. I don't remember how soon after he memo he got the offical letter. We still have it and it was addressed Dec 24th...nice.

But we got it in Jan sometime I think. But, he said it was a mistake that he found out he was getting furloughed through the press release. He was supposed to get some company memo first (not the offical letter though). When he found out about the furlough, he was told his furlough date was for March 1...which was 2 months down the road. Then about a week before that...they pushed it back to March 15.
He was elegable for unemployment and Cobra. But, I did cobra through my job since I had to leave my job so we could move.
His company let the pilots take vacation before they got furloughed, or else they would pay out the vacation time after the furlough. DH decided he wanted the money, so he worked up until his furlough so he could get his vacation time paid out to him. But, his best friend left 2 weeks early and was on vacation the last 2 weeks before his furlough date. As for his insurance, he lost it after he got furloughed. But, we had his flight benefits for about 2 or 3 months after he got furloughed. Besides the money for vacation and the time he flew, he got no other money....that I can remember. But, while he was furloughed, his old company was still paying into his 401K. Kinda crazy we though.
My DH went to Skywest after his furlough. He had to sign a piece of paper saying he gave up his recall rights....but not all airlines make you do that. DH was told by a friend that his old airline was just throwing away those pieces of paper. So, my DH was still in line to be recalled. He actually did get recalled too. He was notified about it through a letter. It was about 3 months after he got furloughed...but he didn't take it.
From what I understand about being recalled, he would have gone back with his 4years still under his belt. He said that if he got recalled now (if the company was still in business) he would go back as an 8th year FO (this is the 4 years he was there and then the 3+ years since his furlough). But this was just his old airline....he said all airline are different and may not do it the same way. His old airline recalled pilots back from most Sr. on down. On the first round of recalls you could either take it or leave it. If you didn't take it, you could get recalled again later. The second time through the recall list, you had to take the recall or you could pass it up basically not longer be with the company. I'm pretty sure once they came back to the company they had to be retrained. To what extent...I don't know.
I'm not sure if my DH was expected to keep in touch with his union/company. I know he kept them updated on our phone #'s and address.
Those are all the questions I can answer. If your DH has any other questions, feel free to have him PM me and I'll have my DH answer them. As I said, every company is different, but my DH can give him some sort of insight of what he went through/learned from when he was furloughed a little over 3 years ago.