1)
How was "va'Ysirem me'Al Panav" fulfilled?
1.
Rashi: They were exiled with hbel.
2.
Malbim: He removed His Hashgachah from them, as if He does not look at their affairs.
2)
Didn't also Shevet Binyamin remain?
1.
Radak: They are secondary to Yehudah, and included with Yehudah.