I do not know at this point. However if you put an unequipped hero in your formation you get a pop up telling you hero is unequipped, the same is not true of putting an unequipped hero into your reserve slot. I put gear and runes on my reserve hero.
The issue I see with reserves getting the "deceased" heroes gear and runes would be in class changes, you would end up with heroes with no weapon and with runes that did not work for them. So at the very least I would put on weapon and class related runes.