On the last level of pathways into darkness, is the thing you're fighting the demon that got released from the vial, or the sleeping alien god? Are they one and the same? I find this unlikely, because why would a god put himself in a bottle? Since it's so close to where you find the broken vial, it stands to reason it is likely to be the powerful demon that was once trapped inside. But you find the gemstone and are able to set the nuclear device, meaning you are on the bottom floor where the alien god should be.
But then if you killed the alien god, why would you still net to set the device, unless he was still alive? The monster you fought could have been some kind of holographic projection of the alien, instead of it being the alien in-person.
Okay, all the evidence is more in-favor of it being the demon. I just find it disappointing that you never even get to see the alien god you're trying to "bury under millions of tons of rock."