This is what happened to Karlag (as well as a mind fragmentation curse given by the demon that caused all this).
Mage burn: Mage burn is serious consequences for casting beyond your comprehension. When a failure is rolled on the concentraion check all of the following effects take place; roll on the insanity chart with no save against the insanity for 1dX weeks; there is an X times 10 chance of aging 1dX + X years; 1dX times 5 percent chance of taking 1dX elemental or spellfire damage; 1dX times 10 percent chance of forgetting ALL spells for 1dX days; 1dX times 10 percent chance of developing a haunt based on the intended spell (DM's discretion).
System: where X = the number of spell levels beyond normal casting capabilities (as in high casting rules). [Ex: a 3rd level mage wants to cast an 8th level spell and fails his concentration check. A 3rd level mage can cast one 2nd level spell at best making the difference 6; X = 6. 1d6 weeks of no save insanity, 60% chance of aging 1d6 + 6 years, 1d6 times 5 %chance of taking 1d6 elemental/ spellfire damage, a 60% chance of forgetting ALL spells for 1d6 days and a 60% chance of developing a haunt based on the intended spell.
The rules for high casting:
High casting: A wizard may memorize and cast spells outside of their normal spell casting capabilities. A 4th level wizard may memorize and cast a (one) 5th level spell by using up all of his non-cantrip spell slots. To memorize in this fashion roll a concentration check DC 20 + spell level. Success means it is memorized, failure means that all spell componnents, items, wands, scrolls, spell slots that are involved in the memorization or casting are lost for 24 hours. In addition, for every spell level beyond normal caster capabilities incurrs a +10% chance of mage burn (described below). (a mage noramlly able to cast 5th level spells -9th level mage- and trying to memorize a 9th level spell incurrs a 40% chance of mage burn upon concentration check failure)
Its not that they aren't supposed to end the quest (its been running a while) or not meet this guy but that since he is fragmented I'd like to prescript the answers and change the response in mid sentence to make it more interesting and challenging.