I'm getting my iPhone 5 6.1.2 replaced - any way to AVOID getting stuck with iOS 7?
It's possible that a refurbished iPhone could run with iOS 6, but it's an extremely slim chance, so I wouldn't count on it. If you do end up getting iOS 7 on your iPhone, there really isn't a way to downgrade to iOS 6 without jailbreaking.

Eventually however, you will have to "swallow the pill" and use iOS 7 (or whatever future update that comes out).