Apparently stock value wasn't affected at all:
"If you work on the understanding that the market value of a company is found through discovery of all information and data, the current price is arguably the effect the market has decided this law suit has on the company. That’s to say until more data is found or discovered.
Blizzard is only a portion of the whole business, but it’s clear the markets aren’t overly worried of any massive loss of subs / revenue at least in the medium term. Unfortunately for everyone here blizzard and activision are large enough to pay and make this go away under NDA."