Hard to say, seat stays are generally quite thick with carbon as most of the pounding is transferred through those posts. I personally would not be worried but you need an expert not a jock to make the call.
That dent is definately a concern,and the carbon tube shape has been weakened by the impact.
The ideal fix is to send the frame of to one of the carbon frame repair specialists interstate and have the tube reinforced with extra carbon cloth and resin.
Regardless of the fact the tubing is not cracked it is damaged and requires a repair !
if you drop it around to my house I am happy to test ride it for the next 10 years to see what will happen :-)
Definetly an excuse for a new bike....