The festival does not end when the chariot reaches Lagan. It ends when the deity is home.
The procession ends at Lagan, where the chariot is pulled three times around the temple housing the mother of Jana Baha Dyah — the same circumambulation any devotee makes on an ordinary day, performed here by the deity at its mother's house. Only then is the image taken down and carried back through the city to Jana Bahal and reinstalled, and the chariot broken down into timbers and stored for next year.
This last stretch happens after dark and draws a fraction of the crowd the chariot days do. It is the part worth staying for. The scale drops from a street-filling procession to a few dozen people walking a shrine home through lanes that have gone quiet, and for once you can actually see the image you have spent three days following.
Related Places & Sites

sacred site
Jana Bahal (Seto Machhindranath Temple)Circled three times by the returning image before it is reinstalled
Deities & Presences
Procession Routes
Part of Seto Machhindranath Jatra