Alternative for is_taxonomy() to workaround theme’s default sidebar

The function that replaces is_taxonomy() is named taxonomy_exists(). Than there’s also is_tax() and is_tag() that check if the query is for a taxonomy archive page.

EDIT

$selected_sidebar_replacement == '0' || $selected_sidebar_replacement == '' won’t work. You’re not checking the type.

Better do it like this:

if ( ! $selected_sidebar_replacement OR emtpy( $selected_sidebar_replacement ) )