One of the (possibly deliberate) implications of the loyalty charm is that it would stop working of the Infernal dies. Given that fomori powers come usually with an equal amount of taints, that means that infernals with fomori minions are loadbearing bosses. If you kill them, their more powerful servants are likely to self-destruct in short order. The power of a fomori is usually dependent on the power of the bane possessing them (with only some niche exceptions), and we're told that if you bind a powerful bane inside someone they generally only last a few days before the fomori burns out (this applied, I think, to other forms of spirit possession as well, it was just evil spirits) because ot all their Taints.
Infernals of course aren't constrained by that with their loyalty charm, but as I say, if they die that protection goes away.
The question is whether Molly would risk her friends' minds, bodies, and souls that way, given what she's just done to two of her other friends…