Function check_replace 

pub async fn check_replace(
    state: &SessionState,
    kind: &str,
    table: &TableReference,
    schema: Option<&Schema>,
) -> Result<()>

Refuse to replace table (a kind) by one with the columns schema while a graph uses it and its definition does not fit those columns. None: the new columns are not known yet, so the replacement is refused whenever a graph uses the table.