A Facebook post suggests that all heritage site have not been demolished. The five storeyed temple in Bhaktapur is still intact so are other temples in Patan and Bhaktapur. A lot still can be seen in Kathmandu apart from the damage done due to the deadly earthquake.
Roads connecting to and from Kathmandu are still operational. The local people at this time of great difficult request tourist to visit Nepal as a support to the damage and victims of the earthquake.
Actually this is the right time for tourists to see world heritage sites in Nepal, and also visit and help the people of the devastated villages in rural areas of Gorkha, Rasuwa, Sindhupalchowk and other districts.
As a proof of this statement this photograph clicked on 5th May proves it all.