"Surely someone has shipped a bike out Ha Noi to Kathmandu?"
Vietnam used to be almost closed for foreign vehicles, the ability to cross at one particular border station is just months old, and I'm hoping its not just some mistake, that they will correct once they find it out.
So I doubt there are many shipments out of Hanoi. I'm sure it COULD be arranged, but price could be a issue, and Bangkok-Kathmandu is about 700-1000 usd for a bike, so could make more sense to go to Bangkok. In fact your shipment could well get routed via BKK anyway. Particularly airfreight moves most cost-efficiently, when you use the big hubs, and places accessible by direct flights from these hubs.