As for the headline, I don't know what Linux lost. Loss implies that you had it at some point, but Linux never really had the desktop, (sadly), so it could not have lost it. It still dominates in the server, supercomputer & embedded markets.
I'd love to peek at the alternate universe wherein Apple doesn't migrate to the FreeBSD-based OSX. In the late 90s I got so worn out with stability issues inherent to Win98 on laptops that I switched to the Mac, largely because a co-worker was using one and I could SEE how much it didn't crash, and how sleep actually WORKED, and how good the hardware was, etc. Since my job at the time was primarily project management…
It’s at least plausible to think that absent OS X, a lot of developers would have made do with then still very rough around the edges (desktop) Linux and, given that level of interest, it would have improved at a greater rate.