That's not a scenario I thought all that extensively about but you can bet he'd go ballistic but in a very quiet and cold way, if that makes sense. Akira is as much a one-man army as Goro is and he knows that—which brings us to what would most likely happen: a suicide mission to kill whoever slayed Goro.
In Arsene's words Thou who art willing to perform all sacrilegious acts for thine own justice!