Some time ago, I discussed the fates of the various cat projects that led to Windows 95, which was in turn a follow-up to a list of cat-related code names from projects that led to Windows 95.
In summary: There were a bunch of projects with cat-related code names. Only one of the projects survived to Windows 95 in its originally-envisioned form. Two of the projects were morphed into other projects that became part of Windows 95. One (Panther) was cancelled outright.
I doubt it.
After all, the Panther project was cancelled early in the exploratory phase of the product that eventually became Windows 95. No public builds were ever released that contained Panther.
You launched Panther by launching Windows 3.1, then going to Program Manager, and double-clicking the icon of a Hallowe'en pumpkin.
I don't know why the Panther icon was a Hallowe'en pumpkin. Maybe the project started on Hallowe'en?
On the other hand, the Panther subdirectory that people are asking about was introduced in Windows Vista, and it is highly unlikely that Windows Vista cared about a long-dead experimental project from over 15 years ago. Windows Vista didn't support upgrading from anything older than Windows 2000; it certainly didn't care about upgrading from an experimental operating system from the early 1990s that never even made it as far as a beta.
From looking at the source code history, it appears that Panther was the code name for what is now known as Windows Deployment Services.
Another case of code name reuse.