Williams led the development of every one of Apple's chips since the A7, which was the first 64-bit processor for mobile devices, up to the 12X chip that is the brain of the latest iPad Pro. Late in Williams' tenure at Apple, he also took over the task of overseeing the layout of various parts of the SoC that the processors he worked on were packaged with. Williams is listed as an inventor on over 60 Apple patents, and while his nine-year tenure is over, his work will continue to be used in Apple devices. At this time Williams hasn't landed at another company according to reports.
While Apple has lost a key processor engineer, it has gained a key engineer from Tesla who focuses on electric powertrains for cars. Rumors have flown for years that Apple is working on its own autonomous vehicle. More recently, the rumors have suggested Apple had decided against building its own car, and will instead focus on software for enabling autonomous driving for other manufacturers. Apple's latest hiring of an engineer from Tesla -- Michael Schwekutsch, VP of Engineering for electric powertrains -- suggests that Apple might eyes on producing its own EV from the ground up.
Schwekutsch's work at Tesla included helping to develop the drive systems for the Tesla Roadster II and Tesla Semi.