They will fix any broken part,
but a missing diamond! No sir.
if it was so, every day they would get 1000's of requests !
you can ask them to replace the missing part and pay for it, they will do it for you in a couple of days.
Also remeber, check the merchindise befor you buy it, if theyput it in a bag, ask them to open it, show it to you, fully examine it then put it back in... as you noticed ... nor Free replacment.