[CerebroDragon]

Thanks, Greything.

I just needed to micro-manage my party's tactics more effectively during the mini-shadows phase to maxmise damage to them and to ensure my spell casters didn't get overwhelmed. So lots of area effect spells, buffing and retreating where necessary to stop them ganging up on one character.

But yes, I have since managed to go on and beat the King of Shadows thankfully. Listening to Ammon Jerro is the easiest way to stay ahead in the final phases as well as a general strategy of keeping the big King Shadow abomination busy whilst others are hacking the statues.
I gave the gith sword to Casavir in the end in order to make the final act of destroying the portal go a little faster.
Here's some final reflections on the group that I had in the end, all of whom were still alive.

PC (Wizard level 19)
Khelgar (Couldn't have done it without him!)
Casavir (Didn't use him throughout the campaign much at all, but he proved critical in the final fight)
Grobnar (I barely used him in the OC, but he ended up being quite handy in his ability to spam Ice Storms, heal and cast great spells like haste and greater heroism)
Zhaejve (Well timed high level spells worked wonders)
Ammon Jerro (Despised him really and didn't want to use him and was frankly surprised that he didn't turn on me).
Sand (Probably my favourite NPC from the OC...was targetted regularly and resurrected a couple of times.)

Looking forward to Mask of the Betrayer, but I'm hoping it's less linear and less forceful on party choice than the OC was...