I think, and I could well be wrong, that the trend for successful companies is towards the latter. None of this is to say the field is bad or will go away any time soon, just food for thought.
You might argue this is just suggesting there is a greater demand for software engineers, and that may be true, but I would be very skeptical of someone saying sysadmins would be replaced. Why haven't we replaced plumbers/electricians? Clearly we have utilities/plumbing/wiring that has been deployed for decades with little to no maintenance? Yet the profession still exists. The reality is, it still takes these tradesmen to build new environments, and support the frequent changes that technology throws us.
I've been through this multiple times. In each case, I hired a good Devops guy and told him to work his way out of a job ASAP. Typically, he was down to spending 1/3 of his time on ops of any kind, including DevOps, within 6 months. At that stage I had him helping Prof Svcs, QA, and the Developers by directly writing product code.
It's true that we'll be able to get more done with fewer sysadmins, but that doesn't mean we'll have fewer sysadmins. The Jevons paradox suggests we might even have more sysadmins.