You wouldn't necessarily need to run anything in Workbook_Open, if all of your users have macros enabled then there would be no need (as the required changes would have been done by Worksheet_Change).

A good way to force people to only use it when macros are enabled is to have a dummy sheet, which simply contains text saying that they need to re-open it with macros enabled. This sheet would be hidden by Workbook_Open (and all other sheets shown), and it would be re-shown by Workbook_Save/Close (and the others hidden).