On most projects, the same team that created the project will stay with the project as it transitions into Support mode. If there is a reason why some staff need to cycle off, please make sure that is clear to the client, and that if a new DRI must be appointed, that is done. Assuming the same team is staying on, these are the things to make sure happens:
Is the client aware that the project has launched? Have they accepted all deliverables?
Is the documentation updated with any changes made during post-launch tweaking?
Is the project todo list totally clear, except for a Backlog of acceptable remaining items?
Have we established an ongoing support relationship with the client? If the client would like a retainer or hourly agreement, do we have a signed SOW? The DRI is responsible for explaining this and “selling” the support agreement. They can delegate this work to someone in sales if they prefer not to run a sales process, but remain accountable no matter what.