Anyway, how do you think Rajaat would stack against some other deities? He isn't technically a demigod, but he would mop the floor with either Iuz or Vecna, even both at the same time.
It says in domains of dread no mortal or demi god can kill Vecna. I suspect this is meant to mean it must be done by a deity higher than demigod status, but if we go strictly by those criteria, then Rajaat can kill him, since he is neither a mortal nor a demigod! :P