Been thinking of doing something similar, I have an Apple ImageWriter and Atari 1025 sitting in my basement. Does anyone know how long dot matrix ink ribbons last new?
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.
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.