Some of them maybe but some require a check in via steam occasionally to run. Steam also recently (due to California's new law) changed the buy page to clarify you are buying a license to the game and not the game itself.
Devs can also at any time issue a command to remove their game from owners libraries (recent case of this being for The Crew)
Devs can also at any time issue a command to remove their game from owners libraries (recent case of this being for The Crew)