This means we have a tendency to forget our most important body of knowledge - the "service organisation". They tend to take over service of the product at go live and then we forget them. Let's correct this mistake in the future.
First and foremost the service delivery manager should be included in the handover of the product prior to go-live. Essential knowledge from the test team must be embedded in the service organisation. Not as a long trivial list of open defects but as story about product quality, workarounds and other necessary information.
Secondly the service delivery manager sits on a treasure trove of knowledge about real user problems and user behaviour as well as technical problems faced by operations. This can be used by the test organisation for a number of tasks including estimation, prioritisation of test effort, general planning of test and as a source for planning test of "off-normal" situations.
The service delivery manager is as such an essential member of the test team. Not on a permament basis but ad hoc at the right time during the project the Service Delivery Manager is your best friend.
If the service delivery manager is not able to provide the input, he is at least the gateway to the organisation where the knowledge is present and available. Just kick in the door.