Wouldn't it be possible to use the same masks to get a basic "shrink", at least for these rather primitive late 80s / early 90s processes? Likely impossible today because of everything being heavily tuned to the wavelength of the lightsource.
It depends on how different were the manufacturing processes.
Newer improved processes usually have some extra masks that would need to be generated, besides shrinking the masks of the original set.
Also, the original masks may need to be shrinked non-uniformly, i.e. by modifying the size ratio between holes and covered areas, not by a simple geometric shrink.
Even when the new masks could be generated mostly by shrinking, there is no chance to make such a complex device work in the new manufacturing process without reverse-engineering it. Correct behavior may depend on timing relationships that would be changed in the new CMOS process and which could require small schematic changes for compensation.
After the schematics is extracted by reverse-engineering from etched CPU samples or from a set of masks, it is probably as easy to draw again the masks as to shrink the old masks, even if the old masks or CPU samples would certainly be used as guidance for the floor plan.
