You can kill off Dynaheir and then remove her from your party and have Minsc stay with you. However, I've found in my latest game that several mages are VERY effective. Mine consists of:
Me - Mage/Thief
Minsc - Ranger
Ajantis - Paladin
Edwin - Conjurer
Xan - Enchanter
Quayle - Illusionist/Cleric
With the number of spells and Wands you can use, almost all enemies will melt out of your path. I have never had any serious trouble in a battle yet (even the big ones) and I'm in chapter 7. If you don't want that many mages then for your party I would recommend:
You - Mage
Minsc - Ranger
Ajantis - Paladin
Imoen - Thief
Yeslick - Fighter/Cleric
Kivan - Ranger
This should be pretty effective, I had one very similar to this and I went through the whole game without too much difficulty.
I hope you find this useful!
-Jafin
------------------
Arch-Mage of the HADB
Destroyer of the evil Bunnies
Guardian of Boo and best friend of Minsc