Assuming that the world continues to exist in a way that lets me have a steam account at the time of my natural lifespans average end (another... 46 years):
My steam library grows at a slower rate than my mass storage has, and I'm quite confident that one will be able to fit my entire steam library as it currently is on a normal and affordable drive in at most 15 years.
With those two facts in play I can remain confident in my ability to crack everything I own (assuming I even want everything) and safely store it for at-will passing down to as many people as I want.
But thanks for the reminder to not blindly trust you, Valve. Always useful to have those.