At least he owns his own domain and can eventually switch over. A few years ago we decided to switch our personal emails from gmail accounts to domains we own (though the email is still handled by google.) This way if we ever lose our google account, we can switch the MX and be able to get all our recovery emails, bank second factors, password recoveries, etc.
They could switch their domain to another email provider and start getting emails, which is great. The problem though, is they also used their Google Account to log in to all the 3rd party services (payroll). I have no idea how you would get back into those services. Some _might_ let you switch off the Google Sign-in SSO, but I imagine that is a headache.