I had a really nice job as network admin / sys admin but, that place fell on hard times and shut down. It took some real doing but, I finally got back into a steady ( not temp ) sys admin job and I'm loving this one even more than the previous one.
Lots of variety from pulling wires, repair copiers and printers, imaging workstations, adding / setup users ....
No worry about the future of sys admins as long as you have users. But, not likely to dump Windows completely because we have some in-house programs which nobody is in a big hurry to change.
At any rate, life is good and I'm paying the bills!