terrible thought - all the ENGINEERS are dead

I'm sorta wondering why the Engineers haven't come back to earth since they (obviously) passed on their PIE or kuniform language down to the ancient Sumerians, maybe they WERE the Ancient Sumerians and have since fled this rock ... I know they were supposed to have come back to Earth 'in the form of Jesus' and whether I like this or not doesn't detract from the fact that THAT WAS THE LAST TIME THEY CAME what have they been doing since? apart from hibernating on LV-223? In a sort of military lock-down? what of the other Juggernauts on LV-223 like the one David and Shaw took off in? does theirs still contain four sleeping Engineers? what happened that the Elder Engineers (pure) became the Engineer Pilots (stained by the Alien skin)? whose writing is the 'more Chinese' on the goo-urns? Do any of the old Engineers still survive i.e. was the Sacrifice Engineer the last of their (dying) kind? Are the LV-Pilots like JIHADISTS or TERRORISTS from the old Empire? I guess there are more questions but it's your turn now...