I tried to farm this on heroic a year ago and never did get the toy to drop, though I did get the boss to spawn.
My understanding was that you could solo it, but like you said, need to finish convo with Eva Sarkhoff. I don’t know that someone with the toy already had to be present?
I don’t know I gave up on it a year ago, but think can solo it and get him to spawn.
Or I’m just not remembering it right.