Yes, they definitely grieve. We lost two dogs last year who had shared a kennel. I know the first one was not quite the same after the other died and she died 6 months later. We had added another younger dog to the kennel which helped some, plus the extra attention, walks, etc. Now the younger one is on her own and seems a little lonely but daily walks, extra attention help some. We just aren't up to getting another dog at this time. It is so difficult to lose them.