I didn't find the Dartan resolution heavy handed at all, to tell the truth - in particular, it sort of "closed the circle" and tied in nicely with Gorgoldand setting up his new "Silver Quill".
One aspect of the high level game which I think you carried off really well was the "Acessiwal playing cat and mouse" angle, which was excellent (even if it was only backstory!).
In my campaign the highest character is 11th, and the highest magic user is (checks) 7th... so I've not had to deal with the plethora of spells problem... but I have to admit that even now I find it hard to balance encounters. Four of the five most recent adventure sessions has had a party death and I wasn't even trying hard to kill them*
As an interesting semi-parallel to Dartan, it is the chap whose mostly fighter who has been the best survivor to date.
One of the things I've noticed about 1st-5th levels - it is quite common for PC's to get wounded and lie there bleeding, but still be saveable. As they reach higher levels that 0 to -10 buffer gets mighty small, and tends to get zapped all in one go.
I bought Bastion, but I don't think I'll ever use it as I can't see how I won't kill all the PC's!
Cheers
* and this is WITH my houserule that says when you go past -10hp, you are allowed a Fort ST (DC= amount below 0) in order to survive hanging there at deaths door. It used to work great, but recent deaths have been facing DC30+ ST's and just can't manage to roll those 20's.