Ally or not, they are under the spell of a terrible entity and must be stopped before there is any further loss of life. You shout for the troops to engage. The unnatural force coursing through your ally's body gives them incredible strength, and they manage to fell several of your men before you can take them down.

With your ally dead on the ground, the shadows recede once again. You were responsible for this person, and now they have paid the ultimate price for trusting you. There is nothing else to be said as you continue on toward the Spire, leaving the corpse behind you.