You can't. If Corey is any indication, the Architect will just use Utha's dead body to reconstitute himself and reappear sometime in the future.
Now, he fights like an arcane horror, so use spell resistance and mental resistance gear. Utha will require physical resistance to blunt her W&S attacks, and armor penetration to produce meaningful damage. A Force Field on her can keep her out of the fight for a while, long enough to hack the Architect to pieces. Flaming Weapons provide additional damage. Honestly, if you've made it this far, they're nothing a full-party hog pile can't fix. RShepard227 (talk)