Ok, well I have a few comments here...first, i agree with the runes up to the mana regen seals, instead i would recommend ability power per level just for that little extra kick.

Also, I would recommend taking the mana pool masterry so that you get an additional 5% of mana which would fuel another whole spell probably.

Lastly, I would dump the guardian angel for a late game lich bane (or move void staff back to last item) or if you need some protection i would say grab a banshee veil for the extra health, mana, magic resist and spell block...if kass keeps dying then you're playing him wrong...

last thing...clarity on kass is a fail, you should add teleport or cleanse to make him more efficient (maybe why you're dying and need guardian angel)