I believe that @User has some experience removing metal layers?

I'm sure that's more expensive and time consuming than just sticking the chip under a microscope, but if somebody is willing to do that for free, then great. . . Nevertheless, other than the fill patterning which in this case SkyWater did for us, it seems that the fact that we have open (or openable) GDS for the chip means that you shouldn't have to go to any lengths to reverse-engineer it.