1)
What do we learn from "Gam Hem Ito Yardu She'olah"?
1.
Radak: The kings who were with him, they were killed via the sword, like him. Malbim: All the kingdoms were conquered and their lands were destroyed.
2)
Why does it say "u'Zero'o Yashvu v'Tzilo"?
1.
Rashi: Ashur's arm, i.e. its helpers who dwelled in its shade. Radak, Malbim - all descended to the grave and were killed via the sword.
2.
Radak citing Targum Yonasan: His authorities were dispersed from their strength amidst his kingdom.
