It is advisable to arrange a conclusion identical to the 'kick-off' of a project. For example, organize a meeting with all Stakeholders, including the Project Manager where at least the Sponser talks. This is also the time for giving awards. Think not of the individuals but also to the team. When much overtime has been spent it is wise to give the team members and their friends a dinner voucher so that the 'home' is not forgotten.
Or, for example, a 'drink' to allow them a moment to interact in an informal atmosphere.