Geez, from what I gather about what you're imagining, Mr. Laser Beam
, it sounds something like Zef Cochrane and Lily were living in a Walking Dead
-type environment, and that just can't be the case. It would be impossible for the likes of Rick Grimes and his rag-tag bunch of zombie-bait to decide to build a faster-than-light ship rather than, y'know, survive
Besides, Zefram was only interested in $$$ - money
. Who's going to pay him for his warp ship if there's no civilization, and therefore no economy, to speak of?
Clearly the world didn't end with World War III, but came close enough to scare the survivors into cleaning up their act.