[{So perhaps you would kill yourself}] that is, destroying yourself {on their tracks}, meaning: after they have left, {if they do not believe in this discourse}, meaning: the Quran, {out of grief}, that is: sadness for them.
Muhammad said: "Asafan" (out of grief) is in the accusative case as a verbal noun (masdar) acting in the position of a circumstantial qualifier (hal).
﴿فلعلك باخع نَفسك﴾ أَيْ: قَاتِلٌ نَفْسَكَ ﴿عَلَى آثَارِهِمْ﴾ أَيْ: مِنْ بَعْدِهِمْ ﴿إِنْ لَمْ يُؤمنُوا بِهَذَا الحَدِيث﴾ يَعْنِي: الْقُرْآن ﴿أسفا﴾ أَيْ: حُزْنًا عَلَيْهِمُ.
قَالَ مُحَمَّدٌ: (أسفا) مَنْصُوبٌ مَصْدَرٌ فِي مَوْضِعِ الْحَالِ.