Note the more frequent use of πάλιν in the Septuagint (LXX) is to with translating the Hebrew verb meaning return. That is also a common meaning in the New Testament when used with a word meaning come/go. Since leaving the Earth again doesn't make sense, πάλιν goes with going to the Father; thus returning to the Father.
⸋ἐξῆλθον ⸀παρὰ τοῦ πατρὸς⸌ καὶ ἐλήλυθα εἰς τὸν κόσμον· πάλιν ἀφίημι τὸν κόσμον καὶ πορεύομαι πρὸς τὸν πατέρα.* (John 16:28, NA28)
I came from the Father and have come into the world. Again, I am leaving the world and going to the Father.” (John 16:28, HCSV)
Use of πάλιν in the LXX; שׁוּב is how a modern Hebrew translation translates πάλιν in John 16;28 The modern Hebrew translation is:
יָצָאתִי מֵאֵת הָאָב וּבָאתִי אֶל הָעוֹלָם; שׁוּב, עוֹזֵב אֲנִי אֶת הָעוֹלָם וְהוֹלֵךְ אֶל הָאָב
ha-Berit ha-ḥadashah. (2000). (John 16:28). Israel: The Bible Society in Israel.
Translated to English: I went forth from the Father and came to the world; returning, I'm leaving the world and going to the Father.