The insert_by_period materialization was written ~2 years ago, and since then, we've improved the way we write materializations. e.g.:

• Better API for relations (or maybe I just didn't use them correctly)
• No non_destructive flag
• Helpful functions like make_temp_relation

Additionally, this materialization doesn't work on warehouses other than Redshift (see dbt-labs/dbt-utils#189)

It's time to give this some love: check out the refreshed code for the incremental materialization as a good starting point.