[Jem]

The drawback to changing from Mage to Bishop at this point is, as Gothmog pointed out, that it takes longer for bishops to level up. OTOH, it would be better to do it at Lvl 9 than Lvl 12.

By changing to a bishop, you gain access to all the schools but there's a caveat: your non-mage spells that you can learn will lag 9 levels behind your mage spells and since you won't have the quick +3 points per level-up any longer, it will take longer to build the other schools of magic up without constant practice.

On the plus side, you will be able to purchase/steal/find books to help you gain the lower-level spells pretty quickly, which will also build your realms. To me that is not enough incentive to keep the original mage, especially since the rest of your characters are only 9th level.

I think you would be wisest to dismiss your mage and make a bishop, concentrating his/her skills on Wizardry/Psionics since you've got the Valk/Lord for priest spells and the ranger for Alchemy spells. As the bishop levels up, put 3 points each into Wiz/Psi and distribute the other three amongst his realms, focusing on Water, Fire, and Mental primarily. You can let Earth/Air lag behind for now and Divine can be ignored until you want to flesh it out. The stat points should go into Int and either Vit or Pie to increase his stamina to cast more spells - I'd recommend Vit so he can get IronSkin once you hit 100, which is always good for a support caster.

I would also recommend that even if your other characters hit 10 a while before him that you wait to level them up until all of them can go at once so he can survive against the higher-level monsters you will be encountering. Remember that monsters spawn in relation to your highest character level, not your lowest.

Lastly, I recommend your bishop be either a faerie or an elf, both of which get the most points for bishops. I prefer faerie myself, in spite of the carrying and armor limitations because they regain SP faster and tend to cast earlier in a round than elves.

I have had two bishops in my party in all three of my games -- one elf, one faery. In both previous completed games, my faery had fewer than 5 deaths by the end of the game while my elf had over 10 and my faerie had higher realm skills and did more damage when casting even though my elf had a higher powercast ability. This was even with reversing the schools they each specialized in from one game to the next.