As long as there are search engines around, SEO will always thrive.
Generally, there are two types of SEO: on-page SEO which deals with contents and page optimizations, and there is off-page SEO which establishes relations with other websites. However, there is a fact that no website can stand without a strong backbone, and apparently, that backbone is technical SEO.
Technical SEO is the structure of your website. It's the thing that's keeping your website together, so you can do on-page and off-page SEO on it.
Without technical SEO, your site should fall apart.