I have an installer, I have the game files
The installer requires a connection to a server that Activision Blizzard can shut down at any time.
Not really. You can install and play SCII without any internet connection at all. You simply lose the ability to gain 'achievements' and you can't play multiplayer (obviously). The solo campaign is completely playable off-line.
IMHO, the achievements are a multi-player feature anyway. Why would I care about them if not to brag about them?
The person who can smile when something goes wrong has thought of someone to blame it on.