1)
What is the meaning of "Hitzmatah"?
1.
Radak: You will destroy him, so he will not have a share in You after the body dies.
2)
What is "Zoneh Mimeka"?
1.
Rashi: One who separates from You.
2.
Radak: One who strays from Your ways.
3)
Is the end of the verse a repetition of the beginning?
1.
Malbim: No. "Rechekecha Yovedu" by themselves. The existence of everything is from Hashem; based on one's distance from Him, he has no permanence, life and existence. "Hitzmatah Kol Zoneh Mimeka" is a punishment via Hashgachah; You cut him off due to his sins.