https://store.steampowered.com/subscriber_agreement/
The Content and Services are licensed, not sold. Your license confers no title or ownership in the Content and Services. To make use of the Content and Services, you must have a Steam Account and you may be required to be running the Steam client and maintaining a connection to the Internet.
But steam some track record for keeping game. Game removed from store (like rocket league) still in library.
No need imagine. Look at wii store down, 3ds store down. People hate it. Also backlash to who? Steam? They dead. Industry? Maybe do impact a little.
Really hope steam at least patch out steam server require to play if they die.