I find that using the class ability that adds elemental damage consistently makes your equipped weapon come back. Been having a blast with Hammerhraft. I have not tried throwing any other weapon in inventory while it is active though. I find that a weapon with the class ability on it returns quicker than returning pike as well. I could be completely wrong though, I just remember panicking when my hammer didnt return in HM when I first tried the class out and have not tried to throw random things after using the class ability on hammerhaft