Someone who can solve a partial differential equation with an hour refresher after ten years but most importantly can identify a situation where a differential equation is useful even if they can't solve it outright is still useful. If they're keeping a zettelkästen level system of notes and can get back up to speed on the specifics quickly but retain conceptual knowledge then I don't see any reason to dismiss them.

One issue our industry has is how to identity a great generalist. Broad conceptual thinking is harder to test and interview for than specialized tasks.