There’s an ongoing effort to understand the SID here
http://forum.6502.org/viewtopic.php?f=8&t=4150
Lots of interesting analog chip level stuff, it’s all new to me as I’ve only dealt with things at the digital level, but very interesting to see how the fabrication technology works in an analog way..
You can probably reverse the masks with a microscope with a little elbow grease. Not trivial by any means, but doable by someone in a garage as a hobby.
The real question, does a fab that can work with that process still exist?