Mages and sorcerers are great and at later levels overkill, so its good to take atleast one along, but if you DO want to do it without their help i'd suggest one trick i learned from soloing(can be applied to party too). As soon as you are in the LOS of a spellcaster he'll usually cast defensive spells, mostly contigencies, now i recon you zip outta his sight and stay away for a while(next room maybe) for some time till you hear his spell protections expire(there are sound triggers), then go out and get revenge
Repeat if necessary!