I think Apple will stay in the desktop/laptop market as long as it's the development platform for their software. I believe it's a core principle of how Apple operates to not be dependent on anyone but Apple. It's why they have all their design and technology in house.
This gives them the immense power to switch suppliers and manufacturing locations and completely control their own future.
Pc-clone manufaturers and brands come and go because the parts are interchangeable. Apple doesn't live in that world and actively tries to prevent it.
Apple might let someone like Samsung, Asus or Foxconn manufacture something for them, but they do all the design themselves to prevent what Compaq did to IBM.
There are a few cracks in that Apple philosophy, in that they use Intel chips and some other PC components for their desktops, but they have demonstrated to be able to successfully switch if need when they moved from Power to x86. They have enormous power because they can believably tell any of their suppliers that they might move. It's why they have their own OS, office suite, cloud, browser, etc.
It gives them long term security and complete independence. This results in a company that is much more agile than it's size and age would let you to believe. It is one of the core reasons Apple is able to do what it does.