For the next levels of Blacksite Area 51, we use the “All your base Belong to Us” trope and the Reborn forces attack Basecamp. Since this is Blacksite Area 51, however, it’s not very exciting. The most that happens is that we get some revelations about the Origins of the Reborn.
BTW, the Gun Leon is holding is the XM8 Sharpshooter, a variant of the canceled XM8 rifle that’s featured in the game.