You forgot to include the two DT's that, most likely, would have been the starters, Trystan Hill and Neville Gallimore
Then there is also their #1 backup at CB, someone who might very well have been the starter instead of Brown had he been able to stay healthy, Kelvin Joseph.
Potentially, on a defense that needed vast improvement over last season, the Cowboys don't have half of their starters against the Chargers. This includes their entire starting D-line.
This is the second year in a row where injuries are so devastating, right from the beginning, that this team will be seriously handicapped when it comes to the possibility of a successful season. I'm not saying they won't have one, it's a long season. I'm just saying the odds are rapidly decreasing as the loss of game time to starters continue to happen.