Delete data records - keep joined data

I was not able to find a better title for this.

Branches          Users             Attendance
-----------------------------------------------
branchID^         userID^           courseID^
branchName        userName          userID*
                  branchID*

Here's my table. Due to company re-structure I need to delete old branches and the users that belong in them. But when my boss wants to see old Attendances he wants to see old userNames even if they don't exist.

What's the best practice here? I'm thinking to add a Disabled column in Branches/Users so they aren't visible on the web page.