Kellhus didn't do that much to help the Ordeal once the battle started.
Yeah, he contested Aurang/ax, but I suspect it would have just observed the battle anyway.
He cut the Horn and delayed the horde, but that wasn't that helpful.
You do have a point, Kellhus' presence might have been more of a factor of
morale than actual help...
I'm not sure Aurang wouldn't have interfered, though. Of course, that might be dependent of what the Mutilated would have his role be in a Kellhus-less Battle for Golgotterath.
Kellhus did stop the attacks from the Sun Lance, if I remember correctly, but were the casualties from that really significant in the long run? The Consult might not have even bothered to use it in this scenario, who knows.
Regarding Kelmomas, I think either somebody would have killed him, or uncaring Serwa/Kayutas/else would not have let Esmenet whine her way into keeping him alive. Emperess or no, she has little real authority even at the best of times, and far less so once Kellhus is dead. No where near enough to keep alive the God-Emperor's assassin. IMO, they'd probably roast him alive over a fire and eat him.
I agree with you there, though maybe not about
eating him. Come on, Wilshire, they were already suffering from the effects of eating Sranc, who knows what eating Kelmomas might do to them.

(I wonder if they could make him into qirri, but that probably just works for Nonmen. Qirri made from Kelmomas would probably only drive one murderously insane anyway.)
I even wondered if Kayûtas and Serwa decide that Esmenet herself, along with Akka and Mimara, are liabilities as well in this scenario. Esmenet and Mimara aren't going to be of any help with the battle anyway. Akka
could, but it isn't at all likely that he will fight for them, especially if their intentions regarding Esmenet and Mimara aren't that great. It's not like one more sorcerer (and an outcast at that) could do that much of a difference anyway. In any case, I don't see things going well for these three...
Re: Impact: its a difficult question. I think as far as storytelling goes, the Ordeal simply must soldier on. Everything is already in motion at this point, and Kellhus has little direct impact on the battle itself. From just the scenario of 'what happens to an army when the leader is killed' point of view, the progression is less clear. The issue though is that they can't get home, and they know it. The only path forward is to die trying to cross Agongorea and let the Consult win, or to die trying to stop the Consult. The Half-Dunyain would seize control still, I think, and push forward.
I see what you mean, and you are right, it's not like they can turn back at this point having gone through so much already.
Would everyone react the same way to Kayûtas and/or Serwa taking charge, though? They were united under Kellhus, but it's not 100% possible to predict how they would react to the change in leadership. I tend to think that
enough of them would fight under the Holy Aspect-Emperor's children just as they would have with the man himself... But does doubt seep in into
some of them regarding leadership? Some doubts might have already been there in their minds, only now incensed by the circumstances. Are any of the Ordealmen bold and/or powerful enough to challenge said leadership?
Especially in regards to Serwa...the general attitude towards women in Eärwa hasn't
truly changed. The changes Kellhus made during his reign allowed for the Swayal Sisterhood to exist and be respected. Does that change with his death? Would this lead to infighting within the Ordeal?