There's a lot of space to keep on expanding the line. Just look at the fan creations, adding not only AOs, Heralds and similar stuff, but entire new expansion boards, worlds, and so on. Last year, the boardgame production of FFG was somehow not so big as usual, but they did a lot of other things (pushing Star Wars games: LCG, X-Wing and the RPGs - remember, they have 3 RPGs scheduled, according to the wokipedia set in three different moments of the civil war timeline; creating a new center; acquiring the cardgames.db and so on). Plus, Kevin left in 2012, immediately after GenCon, and I think this required some extra time to find who could supply him on certain line (just speculating, no idea really, but it seems to me quite logical). After GenCon 2013, we've seen some lines resurrecting / continuing (Wiz-War got an expansion, for example; Talisman got two; Descent is receiving constant support) and some new lines arriving (Eldritch Horror, a game I suppose will see several expansions arriving in not geological times), so that it's like there is quite a big activity on the boardgame front again.
Plus, EH is an interesting game, but I know many people playing Arkham unhappy with Eldritch, and many people who were unhappy with Arkham now happy with Eldritch. So, I see the two games having a wider spectrum of fan, and not interfering too much
As Jackman said, I won't be so worried the line is closed: it's still one of their bestselling games, and as long as a game sells, a company has an advantage in investing in that line. Let's see what happens next, but unless FFG declares it's the end of the line, I keep on waiting, patiently