Proper USB power supplies don't just randomly die once a year, that's utter lunacy.

And what exactly is stopping you from getting any 5V power source or even just rigging up an old PSU with a 10W resistor on the 12V rail and splicing the 5V onto a USB cord? This is a non-issue.

Edit: wrote this before your edit, but still stands. If there's anything to worry about reliability-wise in that timeframe it's SD card corruption, but there's plenty ways around that, whether by limiting writes or using other media.

Edit 2: hostile tone not intended, just perplexing seeing something almost akin to concern trolling done in this manner.