In the past, the killing of the leaders of extremist groups in Gaza or elsewhere in the Middle East has tended to produce only temporary advantages for Israel.

Mr. Sinwar became Hamas’s leader in Gaza in 2017 and, with the Oct. 7 attacks, clearly hoped to set off a wider war against Israel. In the months that followed, while he was known to support an agreement for a permanent end to the war, he steadfastly refused the imposition of any new Israeli conditions.