All data types have their limits. This crisis is nothing specific to Identity columns.  It is related to lack of upfront planning.

Additionally, Microsoft always recommends us to use Information_Schema views and functions to get system data.  IDENT_CURRENT('table_name') will return the current identity value (if available.  If the table doesn't have an identity column, the return value is NULL).

It looks like the author has done some changes to system entries to make the column BigInt. Unless he shares something on that area, this article is not useful.