If your rep drops to very low (1-2) good NPCs will leave the group. At some point in the downward rep spiral and/or after committing certain evil acts Kivan will turn hostile and attack the group but I don't know how far down the rep has to progress to bring this on - I am not certain if Ajantis has a similar script or not.
But the real question is:
Why would you want a paladin in an evilish group to begin with?
One other thing to note - dropping your rep too far (down in the 1-2 range) is also a good way to ensure you will never complete the game. The Flaming Fist pansies will kick your evil patootie eventually and the effects of thier attacks even if you kill them and/or manage to run away will keep your party from making any progress in the game. I'd suggest keeping your rep no lower than 6 to avoid this...
