It's just that without it will be a very sad FS3.
But
really isn't
anymore to begin with, at least in terms of personnel. From every quote I've ever heard from them, it's pretty clear that there was never any fleshed-out idea for what FS3 would consist of, other than a few general suggestions like "planet-sized ships" and "bigger problem." There was no FS3 design document, no fleshed-out plot, no completed script. Unless you somehow get the exact same writers and concept artists from the first two games back together and set them to work, it won't really be the same game even if
does make it.
Now, do I think that some other developer would necessarily be able to recapture the same atmosphere that
brought to the first two games so excellently? Not at all. But there's also nothing saying that they wouldn't be able to. Either way, such speculation is generally useless, since the space sim is all-but-dead in today's market.