When you think “this is terrible, maybe I need a new printer” it is time to change the ribbon…ink ribbons don’t die all at once, their print just keeps getting lighter.

And yes, people bought new printers instead of replacing the ribbon because the print from the latest model in the store looked so much better than what they had at home.

If they're anything like typewriter ribbons of the era (and why wouldn't they be?), a really long time if you re-ink them periodically. I don't think any of my dad's fabric ribbons ever actually broke, and he typed a lot.

EDIT: Not "professional secretary" levels, but a lot. Enough that he bought a Selectric II for use at home.

Do you mean last as in how long until they dry out or last in how much you can print?

It's usually linear inches of text - which depends on how much you're printing.

Yeah print… reading anything from a few months to a year. Not bad for how cheap the ribbons are.