Ramban #1: It is referring to the exile of individual tribes who will perform evil - such as those of Reuven and Gad. ¹

Ramban #2: It is referring to the Galus of all of Yisrael when they are all wicked ²

Sanhedrin 110b #1 (according to R. Akiva): "va'Yitshem Hashem me'Al Admasam" teaches us that the ten tribes will lose their portion in this world and "Vayashlichem el Eretz Acheres", that they will also lose their portion in the world to come)." ³

Sanhedrin 110b #2 (according to R. Shimon): If, after Hashem exiled the ten tribes, their deeds are like they are now, they will not return. If not (because they will have done Teshuvah), they will. ⁴

Oznayim la'Torah: It refers to Yisrael who were exiled from their land and not punished together with it when it was smitten with sulfur and salt - like S'dom and Amorah - because, as opposed to S'dom and Amorah, they were destined to survive.

Oznayim la'Torah: Better they should worship idols in Galus than in Eretz Yisrael, because the punishment for serving Avodah Zarah in Chutz la'Aretz is not comparable to serving Avodah Zarah in Eretz Yisrael, the Palace of the King, which is intrinsically holy.

R. Chaim Paltiel: The 'Lamed' is large to teach that He cast the ten tribes forcefully, past the dark mountains and the Sambatyon river, and they did not return.

R. Bachye: 'Lamed' is the largest letter. Perhaps it hints to the exalted level [of Yisrael] that was cast down at the time of exile. ¹

Ba'al ha'Turim: To teach us that the ten tribes will not be cast into exile in the same way as Malchus Yehudah.

Minchas Shai (citing Midrash Lekach Tov Devarim, 51a): The 'Lamed' is large, unlike any other 'Lamed' in Tanach, to hint at the length of the exile.

Toras Moshe: Without the 'Lamed' (and lacking the latter 'Yud'), the Gematriya of the word is 376 - the same as that of 'Eisav', and the large 'Lamed' teaches us that Torah-study nullifies him. Moreover, a large letter is four times the size of a regular one (Magen Avraham 32:1). Consequently, the Gematriya of four x 'Lamed' equals 120, the years of Moshe, which, combined with 376, equals 496, twice 248 - the number of limbs in a man's body and of the Neshamah

Sanhedrin, 110b #1 (according to R. Akiva): It implies that, just as once the day has gone it will never return, so too will the ten tribes never return. ¹

Sanhedrin, 110b #1 (according to R. Eliezer): It implies that, just as the day becomes dark ² and then becomes light again, so too will the ten tribes, for whom it became dark, see the light once again. ³