He is an expat choosing to return to where he came from. Don't see anything wrong with that!
What seems to be 'wrong', based on reading some of the discussions is:
1. He is being too vocal, and/or
2. His tone is abominating toward the fellow immigrants' lives in the US
He is entitled to his own opinion, like everyone else; and is free to stay (as long as the USCIS is okay!) or leave. But since he is a 'public figure' among many Nepalese, the statements he makes can potentially create an impact to the people, especially those that are not finding अमेरिका the way they had expected.
It's possible that he is trying to come back into the limelight by being vocal.
Or , on the more positive side, this could also be his attempt to nudge others and remind that our motherland is still willing to embrace the expatriates like himself and the rests, and it's OK to start thinking about returning -- perhaps with the intent to influence the fellow Nepalis.
Heard some other artist also declared their return following his farewell.
Whatever the case is, anyone that is lawfully allowed to return to their home country or anywhere else for that matter; has all the right to do so, regardless of the age or personal conditions, as long as they can afford! People come to the US for treatment with various medical conditions; some return and some don't make it, elderlies move from the US (and many other parts of the world) to countries like Ecuador, Costa Rica, and Thailand for the sole reason of retirement. Below site lists 'top 10 places to retire' per the current trend.
http://www.forbes.com/pictures/fjle45kgkl/the-top-25-countries-to-retire-to-in-2015/
This is indicated towards the ones that claim or believe that the returning immigrants are turning Nepal into a "briddhashram". That's a baseless allegation! Retirees are people too, and they can also contribute to the country's economy by spending their savings or whatever their source of income may be.
Whether he keeps his US citizenship is solely up to him and what the two countries' laws allow.
~@~