Thankfully, you have avoided Deathwing's notice. Rhea and the black dragon egg, however, may not have been so lucky...
Notes
Accept the quest and a cutscene happens. The camera pans up to the cave and Rhea walks in...
Rhea says: I'll just leave this right here.
Rhea drops off a scroll, then keeps walking to the back of the cave.
Rhea says: How's my little baby doing?
Rhea picks up the egg, holding it carefully. Suddenly, a shadow appears behind her!.
Rhea says: No... it's... it's you! NO!
Rhea cowers, putting the egg behind her. The camera pans around and Deathwing, in dragon form, sticks his head in the cave!
Deathwing says: You impetuous little whelp... I know exactly what you and the mortal are up to.
Deathwing says: Are you ready to die, dragon?
Rhea says: Yes. Just... just show mercy to the egg.
Deathwing yells: Mercy?!
Deathwing yells: THERE IS NO MERCY! YOU WILL BURN FOR THIS, DRAGON!
Deathwing channels Flame Breath, incinerating the cave. Damage done, Deathwing turns and flies away. The camera follows him, then cuts down to the location where the player is hiding.
The quest completes automatically upon the conclusion of the cutscene.