I have a couple thoughts about Games Workshop's stock dropping 25% in one day.
#1: GW is still profitable. This point cannot be ignored or overlooked. Even with all the issues people have with the rules, the way GW treats independent stores, the price of the models, the endless whining of the internet and the surge in new tabletop games... This company still makes a profit. If they can streamline the websites and find a way to bring their operating costs down to a reasonable level, they should be able to raise their profit margin. GW seems to be going through some transition right now, it hurts their numbers but if the changes work in the long run the short term loss will be worth it.
#2: There will be some changes, but radical changes are not really part of GW's DNA. I doubt they'll eliminate entire armies from the canon. The last time that was done was to the Squats in 40K... and considering the player reaction to that action, I doubt they dive head first into that pool of razor blades again. They may hold some releases as direct order only for the less popular armies, but wiping them off the map doesn't seem likely.
#3: Last point... GW made their name when there was nobody much else in the tabletop business. They showed that you CAN make money selling little models for assorted games. Because of that success (and other factors, like Kickstarter) there are a lot more players in the field. GW now has to complete in the world that it helped create. Change will occur, but competition usually produces a better product... so I'm looking to see what the future holds.