Dude, stock prices are hardly telling of anything. There's so much speculation involved that it doesn't really make sense to frame your argument around it. If you look long term at ActiBlizzard's stock, you'll see that it's been on a constant upswing. The current stock price is roughly what it was in May of 2017. If anything, the markets likely over-speculated what was in store and the negative backlash from BlizzCon simply gave investors the inevitable reality check that was needed. Hell, I'd even go so far as to say that the over-inflated stock prices are one of the compounding reasons Immortal was announced to begin with. (Mobile gaming is, after all, the newest burgeoning market and Blizzard has a track record of success in burgeoning markets.)
And while this dip is definitely indicative of internal struggles within the company I'm fairly confident Blizzard has the chops to learn from this fiasco and make it back to the top. There's just way too many smart fucking people working for the company for it to go tits up like so many cynical gamers seem to be implying these days.