Group users by meta field, with name of meta field as group title

i need to return/echo the name of the department/location for each
group of employees

That is actually a generic PHP/programming question, nonetheless, if you mean an output which looks like so:

Location/Department Name
- Employee/user
- Employee/user
- Employee/user

Location/Department Name
- Employee/user
- Employee/user

Then here’s one way of accomplishing that:

1. Add this above/before the line foreach($users as $user){:

   $current_group = ''; // The current location/department name.
   $sort_by_meta  = $args['meta_key'] ?? '';
   

2. Then add this below/after the line if (empty($user->next_ad_int_user_disabled)){:

   Just modify the HTML to your own liking, but note that you need to properly escape data you’re displaying to the user.

   // If sorting by location or department, and the current location/department has
   // changed, close the current UL, display the location name and open a new UL.
   if ( 'emp_office' === $sort_by_meta && $user->emp_office !== $current_group ) {
       $current_group = $user->emp_office;
   
       echo '</ul>';
       echo '<h3>' . esc_html( $current_group ) . '</h3>';
       echo '<ul class="photo_dir">';
   } elseif ( 'emp_dept' === $sort_by_meta && $user->emp_dept !== $current_group ) {
       $current_group = $user->emp_dept;
   
       echo '</ul>';
       echo '<h3>' . esc_html( $current_group ) . '</h3>';
       echo '<ul class="photo_dir">';
   }
   

Side Note: I don’t know why did you call wp_reset_query(), but if you’ve created a custom loop and you wanted to restore the $post global to the current post in the main query, then call wp_reset_postdata() and not wp_reset_query().