1)
Whose demise will come suddenly?
1.
Malbim: These rebels, if their rebellion and conspiracy will become known.
2)
What is "Pid Sheneihem"?
1.
Rashi: The breakage of idolatry, and the breakage of idolaters.
2.
Malbim: Even if their rebellion will succeed, who knows what calamity will come via their change and the new conduct that they establish - perhaps it will be evil, disaster and breakage. They establish conduct like their desire to oppress, extort and crush the nation.