Yes and from what I've read the remaining choices for the position Yamamoto would have taken as Admiral of the Combined Fleet that you named where just as if not more against the Tripartite Pact. Oikawa was against the idea of war with the United States, but Prince Hiroyasu was also none to fond of the idea himself from what I understand.
But lets say that the Japanese still end up fighting the US (which I think they would anyway just maybe without Pearl Harbor) how is the pacific war changed without Yamamoto leading the way?
The end result? Absolutely no difference.
The specifics are a bit more difficult to decide. Midway is almost certainly either gone or radically altered as an operational plan. Even Pearl Harbor is something of an open question, but if the Japanese were going to try the Southern Strategy it was a given that the U.S. fleet had to be taken out as the first step so some sort of major attack would have occurred.
It is very possible that the IJN would have been both far less effective in the first six months of the war, since Yamamoto's overall battle planning through April was exactly the right one (very aggressive and unpredictable) but would also have survived as a serious threat longer (Midway was pure Yamamoto).
By early Spring of 1943 it really doesn't matter, the USN will gain superiority and will never look back.