I think they still have a tiny bit of consciousness together, with Tsumugi gaining it at the end with the sewing kit. That's some bittersweet yuri, they'll probably both run out of time together, with the last vestiges of human thought linking them, unable to speak. They won't encounter other humans so they won't have the chance to lose control, they'll just, stop working, at some point, probably. The translator was so fucked up for that description btw, very nice work.
Edit: After reading the other work in the same universe, there was a lot of hope in this huh, guess they'll get to see each other deteriorate and go crazy, from a newly turned zombie, and one that recently got refreshed by human food.