After the war. Just as Golda Meir did. Note that the reason Chamberlain resigned was not the mess he had made, but because he was near death from natural causes. Sometimes they last long enough to turn defeat into victory, and are remembered not as the idiot who got into the mess, but as the great leader who won the war (e.g. Roosevelt and Stalin).
If the reason for Hamas success was something Netanyahu had no control (e.g. they figured out not to use smartphones to communicate, and set up the invasion using only paper and oral commands, without using the cell networks or the internet), then the blame will fall on the military more than the politicians.