Although Lark Voorhies nor Dustin Diamond didn't return for the reboot in recurring roles like the rest of the original main cast, Voorhies did appear via a remote video-filming segment in one episode. And Diamond had been in touch with the producers about appearing in Season 2 before his death from cancer in February 2021.
Dennis Haskins did not appear as the former-now retired Principal Richard Belding in Season 1.