إِنْ غِبْتَ فَمَنْ يَسْأَلُ عَنْكَ؟
Translation: If you are absent, who will ask about you?
The reply is interrogative, so response-fāʾ is required. Yasʾalu is indicative, not jussive.
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A Question as the Response
The Jussive Imperfect: Governors, Conditions, and Request Responses
إِنْ غِبْتَ فَمَنْ يَسْأَلُ عَنْكَ؟
Translation: If you are absent, who will ask about you?
The reply is interrogative, so response-fāʾ is required. Yasʾalu is indicative, not jussive.