I am playing orcs and have a rock lobber and a spider rider in my battlefield. After my rider has assigned his damage and damaged been assigned to him (without it yet being applied) can I then sacrifice him with rock lobber?

Does the riders attack damage go through even though he has been sacrificed?
Does the damage assigned to him go through to the capital or is it wasted?

You will deal 4 dommages , 2 from the spider riders power and 2 other from the rock lobber.

The dommage assigned by the defender on your spider rider are lost.