It never really has. I don’t think most people realize that Blizzard has not been independant, pretty much ever.
- Founded in 1991 as Silicone and Synapse by Alan Adham, Mike Morhaime, and Frank Pearce. They did software services, not original products at that time.
- 1993 they became Chaos Studios and were doing their own software like Rock n’ Roll Racing and Lost Vikings.
- 1994 Chaos acquired by Davidson & Associates who were distributors. Name change to Blizzard Entertainment. This is where they made most of the games we know as Blizzard games. Warcraft Ors & Humans, Diablo 1, and Starcraft.
- 1998 Vivendi acquired Blizzard Entertainment from Davidson & Associates. Diablo 2, Warcraft Sequels, and WoW were released.
- 2008 Vivendi merged with Activision which brought Blizzard as a studio under their wing.
- 2013 Activision-Blizzard became independent from Vivendi. Blizzard Entertainment and Activision Studios remained separate but under the ATVI stock holding company.
- 2023 ATVI and all studios under that umbrella (many on the Activision Side) were bought by Microsoft.
So, at no time in their game development days as Blizzard were they independent. Most of the history of the company they have been owned by someone.
As for the original question, if there is consumer interest in the game, there may be a way to continue playing it. Technology keeps changing and means of access can be expected to change as well. Things migrate to new platforms. They have the RIGHT to just shut it down as long as they provide notice to players. I don’t think they will though, at least for a very long time.