Bold! There is a setting for that: disable_emails. You can set it so they are still on for staff.
The setting is designed to facilitate a restore from backup, and automatically displays a banner message that you would need to suppress.
Also I wonder how you would handle notifications. At the moment, notifications via the PWA aren’t supported by iOS. Until Apple come to the party, you would really need to utilise this in order to reach them:
Whitelisted Discourse app with Push Notifications via OneSignal