When I speak about career options to people I lead, I say there is a senior level plateau. At that point, you have to be more intentional about growth. If you want to stay in the field, and you want to progress past senior developer (staying a core contributor is an option!), you need to think about where you are going. You can be a generalist, specialist, or outside of development. Going into management is changing careers, much like going into product development or farming.
If you want to be a generalist, you are looking to expand your influence as you tackle harder and harder problems. Tech leads are generalists. Architects are generalists. All of them have some form of technical leadership to help steer larger and larger efforts. You can also become a generalist that specializes in early startups: you are there to tackle any problem that is in front of the organization until it outgrows the need - at that point you can look for new pastures or help guide the organization while solving smaller and smaller problems.
You can also become a specialist. You learn, in depth, a smaller set of responsibilities, but you can build what others cannot. You can debug and solve problems others cannot. You can be a consultant, or a specialized shared service within an organization. You have options, but mastery is what motivates you, and that mastery can be very valuable in certain situations.
But that is career growth, not planning for the end of your career. Sometimes, that is a parallel track, like management or product. Sometimes, that's retirement. Sometimes, that's moving into another industry. I think that's what the article is talking about instead.