We have Nintex Forms for O365, and we use a List Lookup against a Sharepoint list for our Offices.  The Office list is fairly dynamic, with offices opening and closing often.  The Office list has an Active column, with the values Y or N.  Here's how we'd like the form to work:

1. For new forms, the list should only show Active = Y offices for the user to choose (can do this with a View in Sharepoint or the Filter in the form).

2. For previously entered forms, an Office has already been entered.  User opens the form in Edit mode.  If the Office is Inactive, leave the value in place unless the user clicks on it to modify.  Then only show Active offices.

3. Allow the user to save the form with the inactive Office if it is untouched during the Edit process.

I found this nice blog post on displaying inactive values - Inactivating Items in a List Lookup Dropdown, but the form appears to work fine if the user just Views (keeps the inactive value).  My challenge is, if a manager Edits the form later to add a review but the Office is Inactive, the List Lookup shows 'Please choose...' instead of the previously entered value.  We don't want to lose the history.

Is there functionality to do this, or is this something that needs javascript to handle?  Thanks for any help you can give.