Valve could shut down the servers they run but there are thousands of community servers they have no control over.
Valve could possibly kill the server browser service for TF2 to stop people searching for servers but then people could just connect directly to the community server of their choice either from their favourites or by IP directly.
They could push an update via steam which bricks the game completely but that would piss off a metric fuckton of the userbase when the game is still playable with some precautions in place (playing on password protected servers with people you know)
A shutdown as you are suggesting would only work with a game with published provided multiplayer servers and no community servers.
I know I for one don't want to live in a world with only publisher provided servers, those games regularly have the servers shut down because they are no longer profitable for the publisher/devs leaving any remaing community out in the wind.
Valve could possibly kill the server browser service for TF2 to stop people searching for servers but then people could just connect directly to the community server of their choice either from their favourites or by IP directly.
They could push an update via steam which bricks the game completely but that would piss off a metric fuckton of the userbase when the game is still playable with some precautions in place (playing on password protected servers with people you know)
A shutdown as you are suggesting would only work with a game with published provided multiplayer servers and no community servers.
I know I for one don't want to live in a world with only publisher provided servers, those games regularly have the servers shut down because they are no longer profitable for the publisher/devs leaving any remaing community out in the wind.