Yes it sounds like the nerve has died, you need to keep an eye out for a gum boil (pimple) which will indicate an infection as the dead nerve will decay therefore often causing an infection, the gum boil will drain the pus out, pain will also indicate an infection, be prepared for the possibility that it 1) may need removing, 2) need a pulpotomy (removing the dead nerve chemically) 3) that it remain like that until it falls out naturally.

Thanks for this info - DD fell in August hit her tooth and it was bleeding alot, took her for check at the dentist and he explained about the discoloring but nothing else. The tooth is quite noticeably grey now. No one notices but us though.