What is the fate of the head messenger who deliveres the message to stop the meeting? How do the other members of the tribe react?

The head messenger is killed by Okonkwo with his machete. Okonkwo chops the man's head off.

In a flash Okonkwo drew his machete. The messenger crouched to avoid the blow. It was useless. Okonkwo’s machete descended twice and the man’s head lay beside his uniformed body.

The members of the tribe responded in disbelief..... they were afraid and wondered who he would do such a thing.

They had broken into tumult instead of action. He discerned fright in that tumult. He heard voices asking: “Why did he do it?”