Even out of mana, a mage can always use their staff to fire off a basic arcane bolt. I am not thinking of the damage staffs do. Certainly there are weapons that, if they can be wielded, can do more damage than a basic arcane bolt. I would just suggest equipping the mage with a staff and use the weapon quickslot to equip some other weapon as well. Then you can choose to use a bow or sword or whatever if you choose, but always have the staff to fall back on.
Still, each player has their own vision for their character. It's up to the individual and if Sylvus wants to have a word in one slot and a bow in the other and shun staffs all together, that's up to him.
