A conference is only finished on the last day of its programme for the speakers. For organizers its conclusion simply marks the beginning of a new series of tasks to be carried out. You must take care in particular of three bodies: your institution and any other sponsor, speakers and the research community.
Your institution and any other sponsor
All institutions which have supported your conference with financial assistance have obviously the right to be informed about the conference itself and, above all, to check if and how you spent their financial contributions (not to mention that many sponsors do not make their funds available until they receive these items of information). You have therefore to let them have as soon as possible:
Major academies and graduate schools may have their own forms to fill in, which means that you cannot simply send the same documents to all your sponsors, but you have to adapt your data to the format specifically required by each institution.
A special group is constituted by conference speakers and chairs. If you undertook to cover their travel (or other) expenses, it is a good rule to refund them quickly. Do not forget to ask them for receipts, since you have to present those documents, in your turn, to your sponsors.
A completely different kind of obligation to speakers is the publication of their papers, since it does not only concern the people who took an active part in the conference, but the research community as a whole. However, all your efforts to keep single speakers informed of any progress of the proceedings will be greatly appreciated.
The research community
By organizing a conference you may incur one or both of the following obligations.