What if Soviet spies killed Hitler in January of 1942. Does the war end sooner thanks to a leadership collapse, or later if a more level headed replacement took charge?
Germany was still very strong in 1942 - the African campaign appeared to be going well, most of Europe was under their thumb. I suspect we would have seen a lot of in-fighting within the German power group and it's difficult to say who may have won.
However, if a reasonable leader emerged, then they may have been able to negotiate a peace with UK/US, etc possibly resulting in their being able to apply more forces in the east.