We definitely need another city like Kathmandu as a backup in many ways, and Racheeta has a point. Kathmandu cannot handle the current density of population at all. Once the population is decreased, Kathmandu will then be cleaner.
It's not easy to move a capital overnight to another city, but to start with we may want to have the fundamental infrastructures like government offices and an international airport in the other city. We can move a ministry at a time to the target city, and for ministerial meetings, they can use teleconference.
Maybe we can use one of the Tarai cities for this purpose.
May be Butwal, Chitwan.