Zach was absolutely correct in not sending Daniele home.
Daniele and Dick were the only 2 people in the game that Zach could beat in a F2 matchup. If he eliminates Dani, he's in a scenario where if Eric or Jessica win the PoV, they will vote out either Dani or Dick, leaving Zach with no way to win the game. It'd be a 50/50 scenario. If E/J win veto, he has a 0/3 chance of winnning the game. If D/Z win, he has a 66% chance of winning. Averages out to 33%
Now take what he actually did. He voted out Eric, knowing that D/D were going to make a "deal" with Jameka, a player who they are absolutely scared to death of in the F2. And given D/D's low opinion of his Jury chances, Zach has a good shot at being dragged to the F3 if the Donatos win F4 HoH and PoV. The F4 scenarios are more complicated, since his game isn't over if a D is voted out.
Jameka wins HoH- If D/D win veto - 0% chance of winning the F2. J/Z win veto- 66% chance of winning the F2.
Zach wins HoH- If D/D win veto -33% chance of winning. J/Z - 66% chance.
Dani wins HoH- If D/D win veto - 33% chance of winning. J/Z - 66% chance. (From Zach's perspective, he thinks there is no way D/D will take Jameka to the F3.)
Leaving Zach with a 44% chance of winning the game. Even if Dick would vote out Zach over Jameka (with a Dani HoH and D/D veto), Zach still has a 38% shot at winning. Either scenario puts him in better shape to win the game than leaving Eric in and Dani out.