Btw the Prometheus creature that incubate the Engineer is not a facehugger, it's not even the aliens lifeform that we are talking about here.
The bf got infected with the black goo then transfer to Shaw via sexual means after which she cuts it out of herself before the ''baby'' fully grown. As for what happen to Shaw/host when this creature reaches biological maturity while still inside her is currently unknown but i suppose will also kill Shaw/host.
This baby creature was then trapped inside the room until the showoff between Shaw and Eng in which the creature latched onto the Eng and create a Deacon, which is different from the Aliens we are talking about, even though they might look the same.
Off movies media have also stated that particular Deacon that came out of the Eng body, eventually resides on that planet then self integrated itself to the surrounding as a huge mountain. Eventually another human expedition arrived and explore the planet and eventually found out the mountain they are in along with the ''tunnels'' inside, bleed corrosive liquid.
