While in transit in Delhi, they will get you to look at your luggage to ensure everything is in order before they load it onward to Kathmandu. If you do not hear from the Airlines folks, make sure you talk to them to see all your bags in New Delhi.

If you are travelling on Nepali passport, you can go to the rest area just outside of the airport for something like 30 rupees charge. If you have only 16 hrs. and you do not know anyone in the city, I do not recommend you getting out of the airport. They will rip you off left, right and center if you did. I heard that there is an Airport Hotel in the transit area, but I never saw that. 16 hours is not too long to kill, so I would not bother venturing out in a filthy place like Delhi.