Eat all three, muster all of our resources for a clean sweep of the North.
Remember the rules of the evil overlords. We shall immediately annihilate the present threat, not make traps which could be avoided.
Bad idea.
We're dealing with an enemy that :
a) We don't know the location off
b) We can't follow
c) We can't respond too fast enough.
Any such sweep will only result in their suddenly being an Angel shaped hole in our defenses.
Save the Klrntvs, tell the Duke that Oegorda is behind the attacks.
Have him reinforce Oegorda's militia guards with our battle trained cultists. Go into the city personally and supervise the efficient killing of every guard, raise them as zombies under the control of a few wordbearers and then begin wiping out the town. Use the Klrntvs on any major opposition and to tear down the temple and have any cultists help with the confusion, murdering as many as they can. Have our daughter and brute wolves kill as many fleeing people as possible. Once we have control do the systematic torture thing and burn the town to the ground.
Use the evil to strengthen ourselves and raise undead.
Oegorda is a city with 8000 Inhabitants. You want to fight all those people + the guards + the local priests + the local witches + angel's forces?
That is just Hubris to the extreme, and see what happened in our Eastern campaign.
Devour, devour devour. Ramp up physical might as high as possible, gonna need it for the inevitable confrontation. Make it as painful and torturous as possible, to allow for mental strengthening as well.
For whoever makes a more concrete plan, just tack this onto the end of it. We need to be stronger when the showdown actually happens.
This assumes that we can actually force the confrontation, or that it is inevitable.
The Angel is perfectly happy with slowly destroying our forces, nibbling at our evil here and there. Consuming the Krvlnt's will just cause the Angel to hide untill it all wastes away.
My plan :
Save the Krlvnt's, but not in their current form. Raise them as spirits of smoke and shadow, retaining their impressive mind control powers.
Magic leaves traces. Trace the blizzard back to the person who created it, and attack with full force.