There are a couple of ways you can do this already. My plugin needs at least one chair name & email when you set up a sheet, so that’s where you can add your “default” contact person when you create the list. Then when someone signs up for the chair position, you would need to go back to edit the sheet and swap out your default chair with the info for the person that just signed up.
Also, if you go to the “Email Settings” tab of the Sign-up Sheets settings page, there is a “CC email” field, where you can enter the email address for your manager type person, and that email will receive notices for sign-ups and cleared sign-ups.