You will get arrested in Nepal when trying to come back because you have to show your US passport to board the plane. AT THAT point the Nepali immi agent will notice that you have no stamp on your US passport while entering Nepal. So that means as a US citizen you got in to Nepal with your given up citizenship and passport. The rule is 20 yrs behind the bar n Nepal. Although New Nepali constitution menations the dull citizenship, there are no new rules yet. It would work if in US Nepali could apply visa at the port. For egyptian if you were a Aussie you could leave Australia showing your Australian pp and enter US with ur US pp. That's how most dual citizenship travel from what I ahead found on the web.