Minato Namikaze and Hiruzen Sarutobi were not going to stop the war. That was merely a lie they had told Uchiha Itachi.
What standing did the two of them have? Neither Konoha nor Hanzō would listen to them. If they dared show themselves, Uchiha Fugaku might turn his forces around and attack them directly. Only Uchiha Itachi would believe that kind of bullshit.
Danzo was dead, but Root still existed. Hiruzen Sarutobi knew that Danzo had established the Root Base in the Land of Bears. Moreover, after several years of development, Root had recovered its strength very quickly. He had to use his status as the former Third Hokage to intimidate Root's remaining members, then bring them under his command.
They were still no match for Danzo when it came to building forces outside the village. If they wanted revenge and to set Konoha right, a large force of ninja was essential.
Hiruzen Sarutobi and Minato Namikaze had learned to bide their time when they were not absolutely certain. Their previous surprise attack on the Land of Tea had ended tragically precisely because their reckless impulsiveness had led to the deaths of Jiraiya, Shikaku Nara, and the others.
Hiruzen Sarutobi could no longer get involved in the upheaval in the Land of Rain. The organization he and Minato Namikaze had developed outside the village over the past two years was too weak to compare with Danzo's. Nor could the four clans of Sarutobi and Ino-Shika-Cho offer them much help; Konoha ANBU was no pushover.
Hiruzen Sarutobi could only pass the news to Iwagakure and Sunagakure. If the Land of Fire annexed the Land of Rain, that was definitely not something the two great Ninja Villages wanted to see. Sometimes, sacrifices had to be made for the greater good. This was