I thought most of us figured out loyalty to any specific corporate employer was a dead end back in 2008 (or even 2001 for some of us). The better path is assume the job won't always be there, bank what savings you can to weather the inevitable gap of unemployment (hoping you never have to use it), and take advantage of every training or learning opportunities at your current employer to improve your skills to take the next step up the ladder with your next employer.

I'd absolutely go back to an old employer if the price was right, and in fact, I have. It lasts as long as it lasts, just like any other job whether you've been employed there before or not.