You DO realize that Steam games are easier to crack than any other DRM, yes? That there are websites that have cracks for damned near every game Steam has ever hosted, including cracks for Steam itself so it will just be locked into offline mode forever? That the majority of cracks out there for triple a titles are based on the Steam version because the Steam version is the easiest to crack...you do know this, right? And that Steam has a built in backup tool so you wouldn't even need Steam to reinstall your games at any time?
Worrying about Steam going away is like worrying about CD checks, its technology that has been broken for ages, everyone knows this, but it stops casual copies and helps cut down on cheaters (you can even tell which games have used Steam to crack down on cheaters as you'll see screams of "FORCED UPDATES ZOMFG!" because cheaters had broken the MP on the old version) but keep you from playing your games? Only if you cannot use Google.