For now. As I said, there are ways it could be reopened, but unless the properties were reunited under one company again, they wouldn't be called Horrors, and you wouldn't see any of the same names (i.e. Verjigorm would not be mentioned by name, but you could see cryptic references to a Great Hunter). Hell, apocalyptic cults worshiping Horrors (though they wouldn't be called that, natch) could happen, especially if some poor fool picked up an artifact left behind talking about 'a great scourge' or something similar. Lots of room to have references in the lore, whenever deep dark magic stuff happens. After all, in Earthdawn, some elf found a magic tome that told of the Horrors and foretold their return, went crazy from reading it, and started a magic kingdom to try and stop the end of the world (no, seriously, that's what happened). With the recent artifact rush, rising mana levels, and maybe an alchera or two, it is possible. Hell, we've already got a 'Life Rock' found by the DIMR and what is clearly a T'Skrang (or a changeling that is close enough to be no different) working for Lofwyr. They aren't direct Earthdawn references, but players who know their lore get them. Still, as for actual Horrors appearing in the setting? It ain't happening any time soon without something on the same level of Dunkelzhan's blowing himself up or the Great Ghost Dance going down.