After building the huge list of Apps and Services you have connected with your Google Accounts (https://www.google.com/settings/dashboard) you then have to download whatever is left using the https://takeout.google.com/ Takeout tool.
Once you have this download and have reviewed everything on the Dashboard it’s time to delete the designated account from your Google Apps Domain.
Repeat as necessary. For us we had three or four idle accounts in our Google Apps before cleaning this up. For the ones that are necessary you can move the Data to another account that you can control – within the domain. I’m not sure how to move data to an account outside the domain.