I'm really sorry this is happening,
I hate to think about leaving Blogger, because I like the way it works, and I want to like Google. But this experience has made me look at the other options. Every hour that passes without getting the archive back erodes my confidence. Perhaps Blogger really isn't meant to handle very large archives. Some time ago the "manage posts" page stopped working to return search results further back than about a year.
ADDED: I'm not going to keep this post bumped up to the top. It's too tedious to see it, and it makes the stuff below it look old. So... this is all very annoying, but I think I'll recover the whole archive soon enough... and this has lit a fire under me to make a big change that I think you're going to love!