Any staff members without a Business Role won't be able to log into Arbor. There are two ways you can check for any staff who don't have a Business Role.
Staff who used to have a Business Role
Follow the instructions in this article to create a new report: Creating bespoke reports in the Custom Report Writer
Select that the report is about Staff, and set the date range as last year.
Add a column for Business Role and set the date to Today.
Skip the rest of the setup, then add a filter for Business Role. Set the date as Today, and select Is empty/blank.
You can then identify any staff that had a role last year but don't this year. If they've not left your school, you can assign them a role using these instructions: Adding a Business Role to a member of staff
Any staff without a Business Role
Go to School > All Staff > Browse Staff and put it into list view. Click into the filters and select All Staff.
Click the Business Roles column header to sort all your blanks to the top. If they've not left your school, you can assign them a role using these instructions: Adding a Business Role to a member of staff
Top Tip: You might need to go through each page on that screen due to the way that sorting works on tables in Arbor.