I recall reading somewhere that all mail order only minis are "cast on demand". They don't just keep churning out metal Catachans and Valhallans either.
The more obvious sign that
GW does not plan to do away with them anytime soon is the revamp of their store page, as well as the release of
WD articles. The new Minidex is a crutch, but there was no reason why
GW should have invested any resources at all into this army if they just wanted to let them disappear.
They may not plan to get them a proper Codex or revisit their miniature line (I'll believe those rumours when I start seeing official announcements), but at the same time there is absolutely no reason to assume that they would suddenly pop out of existence just because a few haters keep proclaiming so since about five years.