Just for the sake of clarity, since you've only gone to mention at what point we are looking at Night Haunter, are we to assume that the Corax for these is post Deliverance Lost
and has come to terms with stymieing the traitors rather than outright defeating them?
Konrad Curze and Corax are each released into an unknown city, they are both tasked with killing the other primarch. This is Konrad Curze post of "Unremembered Empire", thus he has his "precognitive spidey-sense".
I think this one is rather even, because while Night Haunter may be rather good at setting up a battlefield to suit his purposes Corax has excelled in fighting guerrilla warfare his entire life.
Both Konrad Curze and Corax are inside a football field, they are both to fight to the death
Night Haunter, assuming there is no escape and the two must fight. Corax did not believe he could defeat Night Haunter on the killing fields of Istvaan, nothing has really changed since that.
Instead of the Lion with the Dark Angels battling Curze in their isolated sector war it is Corax and the Raven Guard, which legion wins the war? (Corax does not get the Deus Ex Machina that the Lion received)
Assuming this is post Istvaan, then the Night Lords would win. They outnumber the Raven Guard in legionaries and ships, they can bring overwhelming force against the Raven Guard ina lmost all engagements.
Not exactly the fairest of scenarios to be honest.
Konrad Curze is tasked with killing the primarch of the Blood Angels, he has his full legion to accomplish this. Corax is tasked with killing the primarch of the World Eaters primarch, he has his full legion to accomplish this. Which primarch is successful, and or are both primarchs successful?
I think Corax has a better chance of being successful, if only because the World Eaters would be easier to manipulate than the Blood Angels. Ultimately I do not think that Night Haunter would be successful in taking out the lord of the Blood Angels.
Konrad Curze and Angron versus Sanguinus and Corax in a fight to the death.
I think Corax and Sanguinius would defeat Angron and Night Haunter. As before, Angron would be easier to manipulate and Sanguinius is often considered amongst the best of the fighters amongst the primarchs.
The Night Lords legion with that of the World Eaters engage versus the Blood Angels Legion and the Raven Guard. The fight is to see which team can eliminate the other team, the war takes place in the sector that the Night Lords fought the Dark Angels.
Again, Night Lords and World Eaters lose largely for the same reason as in the other scenario's. The ability to manipulate the World Eaters would cause them to take more losses than they would likely cause and both legions general inability to work together would likely be a hindrance. I can't imagine the World Eaters always showing complete restraint if the Night Lords got in their way.