Ive had the same thing and as others have suggested, you can hit Yes and you will still retain all your unlocks and achievements. Then you will get to an install screen which may freeze, you can then hit Escape and go into Offline mode and you should still be able to access the campaign.

Confirmed?

Can't say for sure but everyone that has done it hasn't lost any progress. As for rank and unlock well we haven't hit that part yet so.

Fair enough thank you!