Does my Retirement KITAS or Retirement KITAP expire when I leave the country?

No. The Retirement KITAS and Retirement KITAP are multiple-entry permits, meaning you can enter and leave Indonesia as often as you want during the validity period.

Your KITAS/KITAP will not expire automatically just because you travel abroad.
It only expires on its official end date, unless cancelled intentionally (e.g., through an EPO).