Using a lost iPhone 5 on iOS 6?

I lost my iPhone 5 or possibly had it stolen yesterday. It was on iOS 6, so no Activation Lock yet. On Find my iPhone the phone appears to be offline. If the thief does a hard DFU reset on it through iTunes, could he possibly use it again? I know that if it was on iOS 7 and it had Activation Lock it would be a paperweight because the thief wouldn't be able to activate it without an Apple ID and password. But what about iOS 6? If it's restored via iTunes can it be used again?

I don't think I'll be able to find the phone, and would be happy to know that a thief would not be able to use it.

Should have updated it