A Mule application deployed to a standardalone Mule runtime uses VM queues to publish messages...

In case of a system failure, in-flight messages in persistent VM queues that have been consumed will be processed after the system comes online. This is because persistent VM queues store messages on disk and guarantee delivery even if there is a system crash or restart. Therefore, any in-flight messages that have been consumed but not processed will be recovered from disk and processed when the system is back online. References:https://docs.mulesoft.com/mule-runtime/4.3/vm-connector#persistent-queues