I assume that if Hitler died before World War II Hess would take over. If Goering assumes power that means that Hitler lasted until after Hess left for Britain.
Oh, I think Hitler had laid all the necessary groundwork by 1923; have him caught with a brick to the head in the ensuing scuffles, and Fat Hermann picks up the reins of the Nazi Party without a hitch. Heck, Hindenberg would probably be a lot more comfortable naming him Chancellor etc. Hitler makes a much better martyr for the cause than he does an actual leader.
The possibility of WWII under Goering is an interesting one. He's more aware of the dangers of engaging Britain, but lots of people were spoiling for a rematch or militaristic types wouldn't have won the elections. He'll try to figure out how to get into a war with Stalin without involving Britain.
How would he handle Rohm?
I think the idea that there would be no Holocaust is wishful thinking. Working slaves to death over the course of 5 or 10 years is just as final as the ovens, and likely to be just as thorough. More so, because Goering might actually win, or wait to start a war until it was finished.