What makes you think the Night Elves want to let the Horde have another crack at killing their favorite demi-god. Horde has already killed him once when they first engaged.
The Wild Gods are not at the service of the Night Elves or any other mortal race. They only come into play when the whole of nature is threathened. Faction disputes do not qualify. They’re animals in mind, they’re mostly not even aware of the Faction War.