The assumption that Macs go away is the assumption that people stop needing to do the things you can currently only do on a Mac. So I don't think your hypotheti

The assumption that Macs go away is the assumption that people stop needing to do the things you can currently only do on a Mac. So I don't think your hypothetical is possible. Either iOS gets more capable, or Macs don't go away. Hell, Apple offered an update to the Mac Pro recently, and we know that doesn't sell as many units as the iPad.