Ahhhh but Ilos was a secret Prothean "base", even in the Prothean cycle the settlement on Ilos was just a myth or a rumor. It was utterly isolated from the rest of the galaxy, not showing up on any star charts as it was absolutely shrouded in secrecy. Ilos was completely "off the grid" as far as the information network was concerned, and that's why the Reapers never found it: when they snatched the Citadel and gained access to all Prothean records and data, they found the location of every single colony...but Ilos was never in the records, as such it was left untouched.samgdawg said:Actually it IS possible to hide life from the Reapers. The facility on Ilos managed to hide the Protheans who were hiding there until the Reapers had all left back into deep space.RJ 17 said:The Zerg thrive in harsh wastelands and would likely sweep across the planet like a flood of death.
The Reapers - in their unstoppable quest for total extinction genocide - would hunt down the humans just because it was their turn to be harvested and the Reapers are incredibly thorough. If they knew there was life on Wasteland Earth, they'd still go there to snuff it out.
As for Javik, the only reason he survived was because the Prothean orbital bombardment buried the chamber his stasis pod was in.
So, under the assumption that the Reapers know where Earth is and they're attacking it (as the OP suggested: "(insert villainous race here) shows up and starts attacking") there's nothing the Fallout humans could do to stop'em.