They won't. Just as most modern devs can't edit assembly and would take days to write a bare bone network communcation, they won't need to learn certain things we did. And they will excell in other skills, making some old aged senior devs obsolete.
A senior that uses modern dev tool chains will allways have a huge edge. That has allways been true. But that senior relying only on their hard earned knowledge will become the kind of dinosaurs we knew when we started.