There are DLLs that remove any check of Steam running. Just keep a copy of one and use that on other games.

Regarding the download, it's the same issue with physical media. If I don't have the DVD, how can I acquire the game?

Oh there are Dlls? And as a non-technical consumer I just know this do I? I know how to dig deep into my file system and copy+paste a dll file into software I can’t/don’t understand? How do I download and install a copy without Steam?

	▲	inigyou 16 minutes ago \| parent \| next [-]
		Has the barrier for non technical consumer gone down? Back in the 90s when some game didn't work because of some weird issue (we had two CD drives and it would refuse to detect the CD in either drive) my parents had no problem downloading a pirated one that didn't need a CD. You wouldn't have to figure it out yourself. They didn't need a hex editor. But they did understand "download this file, go to this part of Program Files, move the downloaded file here and agree to overwrite". You'll find similar guides online. They already exist, because it's the same as if you're trying to pirate a Steam game! People will do anything for the dancing bunnies. Both good and bad.
	▲	saghm 2 hours ago \| parent \| prev [-]
		The premise of this hypothetical is Steam's servers going away. Ping me about this if and when it ever happens and I'll write you a tool where you can select the steamapi.dll you downloaded and have it copied to where your games need it. There's a fair chance you might not even need to because someone else will have made it before me.