In the auto industry, when the first industrial robot came onto the factory floor decades ago, assembly line workers were in much the same position as network engineers are today. They wondered, "Is my job safe? Will I be replaced by an automated machine?" The robots can weld and assemble very heavy car parts with ease. They also do it precisely every time without the need to take a break every couple of hours.
Today, robots do many jobs in auto factories, but they don't do all the work. Some tasks require a human touch, such as putting in a windshield. It's a delicate job that robot arms aren't really designed to do. Upholstery work is also still largely done by people. These specialized jobs that show where humans have flexibility and a certain ability to adapt to changing conditions, allowing them to do the job like no machine could.
In the data center, there still are going to be jobs for people, but certainly there won't be as many as before. Server administration formerly required huge teams of OS-specific folks to tune and tweak each server for a given program. Now, virtualization teams can administer a range of hardware and operating systems with ease. The application work is left to the developers.
Network engineers are going to find a similar trend. With much of the work being done by scripts and automated systems, the mean time to complete a service ticket will indeed go down. With more work being done by fewer people, there will be more competition for jobs.
[Software-defined networking is expected to impact the industry in many ways, including driving up service agility and revolutionizing the traditional IT security model. Check out the slideshow, "10 Ways Software-Defined Networking Will Change IT."]
That won't be the end of the road for the best network engineers, though. People are still going to need to troubleshoot issues and translate developer needs into network and security resources. Automating that process will reduce some complexity. But someone has to automate it in the first place. The seasoned admins are going to be on the front lines of troubleshooting fabrics and implementing policies that provide performance increases. Highly trained professionals can't be replaced by if/then scripting.
Network engineers are also going to need to be around to explain why the system did something in a particular way. If the programming of the system allows it to fail all links to a slower backup site during production hours, someone will need to answer for that. If nothing else, the old-guard networking people will need to be present to prevent mistakes like that from happening in the first place.
SDN and network virtualization will create new challenges and new opportunities. New technologies need to be maintained just like any other system. New systems need knowledge to work properly. The limits of SDN and network virtualization must be transcended by someone flexible enough to overcome them. It’s possible the playing field for network engineering jobs will shrink because of software-defined networking. The key to staying on the field is knowing how to play your game better than anyone else.