כִּ֣י יָדַ֗עְתִּי אַחֲרֵ֤י מוֹתִי֙ כִּֽי־הַשְׁחֵ֣ת תַּשְׁחִת֔וּן וְסַרְתֶּ֣ם מִן־הַדֶּ֔רֶךְ אֲשֶׁ֥ר צִוִּ֖יתִי אֶתְכֶ֑ם וְקָרָ֨את אֶתְכֶ֤ם הָֽרָעָה֙ בְּאַחֲרִ֣ית הַיָּמִ֔ים כִּֽי־תַעֲשׂ֤וּ אֶת־הָרַע֙ בְּעֵינֵ֣י יְהוָ֔ה לְהַכְעִיס֖וֹ בְּמַעֲשֵׂ֥ה יְדֵיכֶֽם׃
Porque yo sé que después de mi muerte, ciertamente os corromperéis y os aparteréis del camino que os he mandado; y que os ha de venir mal en los postreros días, por haber hecho mal en ojos de SEÑOR, enojándole con la obra de vuestras manos.
Rashi
אחרי מותי כי השחת תשחתון [FOR I KNOW THAT] AFTER MY DEATH YE WILL UTTERLY CORRUPT YOURSELVES — But, you see, as a matter of fact, that all the days of Joshua they did not corrupt themselves, for it states, (Judges 2:7) “And the people served the Lord all the days of Joshua”?! (How, then, could Moses say that they would corrupt themselves after his death, by which he evidently meant immediately after his death, cf. v. 16)? But we may derive from here that one’s pupil should be as dear to him as his own self: — it appeared to Moses that so long as Joshua would live it would be as though he himself would be living (he thus alluded by the words “after my death” to a period after Joshua’s death).
Chizkuni
אחרי מותי . It is a historical fact that during the life time of Joshua and the elders of his time who survived him, the Jewish people remained absolutely loyal to G-d and His Torah. (Joshua 24,31)
Ibn Ezra
The word befall, ending in a tav, is the third person feminine singular of a lamed-’alef verb, as in “it is your nation who has sinned” [Exodus 5: 16], as I have there explained [comment on Exodus 5: 16].