If Dissolve was targeting Archon, the Archon goes to the graveyard, but the heroic trigger definitely still happens (it specifically triggers on casting, not resolving the spell).
Whoops, sorry, it was Disperse, not Dissolve. And she cast it targeting the Phalanx Leader.
The heroic trigger would have been nice to get off, but I don't think it would have changed the outcome much. Still, was nice to see what were essentially two armies face off.