It's very hard to believe a studio when it claims work never begun on a piece of downloadable content until after the main game was finished, especially when that DLC is a direct continuation of the story and was essentially teased at the end of the main campaign. Even if nobody started building code for it, it's clear the developer already planned it and was making notes well ahead of time.
Dead Space 3: Awakened picks up right where Dead Space 3 left off, and reveals major plot points one would have expected at the end of the actual campaign. Its main story is so integral to the Dead Space story, in fact, that to play it would almost be seen as essential.
Almost, but not necessary, it turns out. Because, for all the promise Awakened has, its relevant events could be explained in a single sentence.