Steam, one day, will disappear. Not tomorrow, but perhaps 100 years from now. On that day, you will no longer be able to download or even play those games for more than a few days.
That's a sad response. Video game preservation efforts are ongoing for games older than the NES right now, I don't see why that wouldn't be the case in the future for the current generation of consoles.
The cynical reply to this is also "Will I be alive to care?".
A more realistic reply might be "will any humans even be alive to inherit my game library?" or "will anyone even be able to run any of my games on the hardware and software available 100 years from now?"