Your old Nepali citizenship gets voided as soon as you have acquired citizenship of a different country.

Under new constitution, you can apply for a citizenship specifically designated for those that have acquired citizenships of countries outside SAARC region. 

This will allow you to enjoy all the rights of a Nepali citizen except being able to get politically involved (no voting).

But unlike NRN card, there won't be any economic restrictions. You get to enjoy all other social and economic rights (purchasing land and property like an average Nepali) under new constitution. 

This should also allow you to apply/acquire a Nepali
passport and a dual citizen should no longer be required to have a visa to live and work in Nepal.