It is not good if you let the DEF tank run out. I have a BMW 335d with 5000 miles and have not had to fill the tank, but the owners manual said it will give a warning when you have a 2000 or so miles left. It continues to give warnings, but if you ignore the warnings your top speed will be reduced and after the last warning, your car will not restart.
I think a diesel in the Cruze is a great idea, but the DEF tank will need to be filled and not ignored.