I like mages, they are suicidal though.
Use them early on some missions and they level nicely off the smaller dens.
At level 5 they get the shield which helps significantly.
Their Ice Arrow or whatever needs to be a priority and to a lesser extent the whirldwind spell, both have defensive benefits. (Cloth armor is always my first pick for the blacksmith.)
Grouping them helps a lot. 2 clerics guilds(or three in some cases)
When you aren't using groups they tend to respond to lower values then healers and some melee. You can ramp up the gold for attack flags to get more responders and/or use fewer outstanding flags. Placing a lot of flags at once will spread out all your groups which ups the mage suicide rate, have your next mob/den attack flagged and add gold to it as the current den or mob is just finished being killed.
If you do build a guild just for the weapon enchantment; get the magic shop, even if you don't buy any potions it makes a few hundred gold a day if I recall correctly.
I have had similar issues with elves getting them their various skills helps as well as using them early. I love putting them with a paladin lead with a pirest of Agrela and cleric, the elves tend to share the speed boost in party the most and the paladins are eager responders to stronger mobs.
I have used mages without a single mage death on some of the harder single missions, but not with any conistency, but what do you want they are supposed to be squishy?