If they weren't listed as sold out before he mailed it they will TRY to honor the order as best as they can. If they cannot they won't, but they do their best. They might do what they did with you and offer the upgrade.
I placed an order years ago for a SG Springfield. They emailed me and said they were not finding many SG's and offered me a SG Winchester that was not even available to order. I got the Winchester.
Yeah, depending on how many unfilled orders there are before me - I could be SOL. Maybe they'll be generous and just put me on a waiting list - and as they crack open some more crates, maybe there will be a Winchester or two? Here's to wishful thinking. The auctions are a bit too rich for me, and I was really hoping to round out the 4th manufacturer for my collection!