How effective is Israel's policy of killing Hamas leaders?

The policy has been so effective that the successor to Rantissi is being kept secret.

Faced with an Israeli threat to kill all leaders and operatives of Hamas, the movement has decided to keep the name of Rantissi's successor secret, a Hamas source said. From ABC News

I doubt it will make much difference; the Israelis already know the likely candidates.

Palestinian sources speculated that possible successors could be Mahmoud al-Zahar, a senior Hamas leader who escaped an Israeli assassination attempt last year, or Ismail Haniyah, Yassin's former right-hand-man.

If I was either of these guys I would be afraid, very afraid. You guys might want to try and think out of the box and maybe try peace.