Why was the verb "لَنُخْرِجَنَّكُمْ" (we will surely expel you) put in the jussive mood, while the verb "لَتَعُودُنَّ" (you will surely return) was not, even though they are in the same verse (Ibrahim: 13) and use the same lam (particle)?

This 'lam' (ل) is not one that causes the present tense verb to be in the subjunctive mood; rather, it is the 'lam' of an oath, which does not make the present tense verb subjunctive. "Lanukhrijannakum" (لَنُخْرِجَنَّكُم) is not in the subjunctive mood but is built upon the 'fath' (short 'a' vowel) due to its connection with the 'nun' of emphasis (nūn al-tawkīd). As for "lata'ūdunna" (لَتَعُودُنَّ), it is an inflected verb in the nominative case. It was not built upon a vowel because the 'nun' (of emphasis) is not directly connected to the verb, as it was separated from it by the 'waw' of the plural (wāw al-jam‘). It is in the nominative case, and its sign of being in the nominative case is the 'nun' that was omitted due to its meeting with the 'nun' of emphasis. Similarly, the 'waw' of the plural was omitted due to the meeting of two silent letters. The present tense verb is inflected (i.e., not built upon a vowel) if it is free from a direct 'nun' of emphasis and the 'nun' of the feminine plural.