Hey Kassemanwar,
First and foremost congratulations for making that far. This are stories that give me hope to continue applying for UN. Personally I work with the government in my home country. If the job offer is permanent you should take it and resign from your current job. You should calculate the benefits viz-a-viz the exposure you will get. The benefit which I will get after working with my home government for 27 years is equal to UN two years pay. You should not be afraid for the unknown……