It appears that on the timeline, by 2016 AD, the Megaroad-01, shortly after colonizing Eden, it has lost communication after getting closer to the centre of the Milky Way galaxy. We all know that there's a supermassive black hole right there, and if they veered too close to there, everyone on board, as well as their escorts were fatally sucked in for good. Or a separate Zentradi group, different than those that threatened the human race 8 years ago, had engaged into a surprise attack in which no VF could ever withstand (Megaroad's no battleship of its own!)
Now the question is, how did the Megaroad-01 disappear from existence? Vote it here!