In my experience, mice don't really break since optical tracking replaced rollerballs.
What does happen is that the exterior gets grody and the glidepads wear out.
A true "forever mouse" would be one where the stuff that gets worn out is easy to clean or replace. Ideally the tracking unit itself can be replaced, although that might be excessive.
For Logitech to produce a mouse like this, however, would require them to make a multi-decade commitment to supply parts and specs, which is basically just a cost sink in today's world.
Thanks for the link, I did not know about this outfit (and jeez, I know naming stuff is hard, but "Ploopy" is kinda bad as a company name).
While I appreciate what they're trying to do, the aesthetics are very much "hackerspace afficionado". Logi could presumably bring premium materials and finishing to a "forever mouse".