If all that's needed is a forum to communicate, then just outsource its function to a corporate meetings planner.
Have a UN meeting four times a year at various locations around the world.
We don't need a permanent, entrenched bureaucracy with arrogant aspirations to being the world's highest government authority, and the power to levy taxes, raise armies and control the Internet.
The only thing worse than the UN's ineptitude is the horror of having it be empowered and efficient.
The question will be what is going to be a clever alternative to the UN without losing the claim to be really global. As I already said, a solely American solution will not help, since the nations who would take part will not represent the whole world. Nations like China, Russia, Japan, Germany, France, India, the UK and Brasil have simular interests like the US. They need a safe basement for trade and their security. Therefore they will help the US if they share its interests. For this kind of help the UN is still a working frame. Smash it would mean, that there will be no continuing contact between the leading nations in this world. This would be a high price for the satisfaction of kicking Kofi Annans a**.
Right next to being empowered and efficient is empowered and INEFFICIENT, or an even greater black hole of money and resources with the power to tax and make people wear the blue helmet whether their goobernments like it or not.