||the shops and mechanics will increase in numbers. There are lots of Z knowledgeable independent garages nation wide already, and some will become more professional in their marketing to the Z owners needing work. As parts dry up, new parts will get made. Even today we are seeing guys w/ 3D printers, those modifying alternative Nissan parts, and home garage businesses beginning to fill the void. It might not be cheap, but the parts will be available.
However, those owners not in major metro areas will be forced to ship the cars in for major service. Look at how Jag E-type owners handle their maintenance. Some E-Type owners are DIY, but most ended up working with specialists. Those shops also handle a number of other marques, like Austin Healeys, and Jensens, etc. Likewise the Z shops will fix Skylines, Supras, 3000GT4. etc. Whatever they need to fill the bays in order for the shop to turn a profit.
There has always been this 30 year shift from factory dealer warranty work, to Indy shops, to the marque specialist shops. The first Studebaker coupes came on line in 1953; yet still today, I can buy a rusted barn find and locate almost every part I need to finish the car. Studebaker specialists are still around, some the sons or the original mechanics. Anyone who owns an 50 year old antique auto knows the resources available through the network of other owners. Something popular like a Model A can be built completely new from the frame up by using aftermarket suppliers and vendors. Not saying the Z32 will ever reach that level of popularity, but once the parts cars a pulled indoors and inventories of select items are better preserved, you'll see a second wave of part suppliers come on line.