Thanks for this , I asked because of similar experiences ( although not involving parallels runways and in airports far smaller than KIAD ) . I was clear to take off on a small GA aircraft from a large airfield and once airborne was following ( overflying in fact) the runway center line as per the SID. when the following aircraft (an A320 ) was ordered to go around and the discussion started on the frequency as to what we should do, as obviously a straight ahead go around as the chart says would make things worse, and we both had no visuals on each other.
Another time I was watching from the ground an ATC TWR radio failure situation , where the aircraft already lined up for a while waiting for the preceding landing to vacate, announced he was taking off ,The one on finals had changed frequency trying to reach the TWR and decided to go around ,seeing the aircraft lined up but unaware it was taking off. Both flew straight ahead, ended up exactly one of top of each other at the end the runway fortunately with a few hundred feet separation. There is a clear loophole in those go around situations, but as I was told at the time , you cannot regulate everything,