What is the replacement for rich_edit_exists()?

This is stored in the user meta table under the rich_editing meta key for each user.

You could one of these (untested):

1) Add it for your specific users, e.g. via

`add_user_meta( $user_id, 'rich_editing', 'true', true );`

2) Within the wp_default_editor() function, that determines the default editor, the user_can_richedit() function is applied.

It checks for get_user_option( 'rich_editing' ) === 'true', among other things.

It’s filterable through the user_can_richedit filter:

    /**
     * Filters whether the user can access the rich (Visual) editor.
     *
     * @since 2.1.0
     *
     * @param bool $wp_rich_edit Whether the user can access to the rich (Visual) editor.
     */
    return apply_filters( 'user_can_richedit', $wp_rich_edit );

3) Try to filter the get_user_option( 'rich_editing' ); if it’s missing.