The following figure illustrates the failover DAS and failover Node Agent configuration after a node failure.
After a failure on Node1, resource groups RG1 and RG2 fail over to Node2. Resource group RG1 contains the DAS and its failover address IP1. Resource group RG2 contains Node Agent NA1, instances I1 and I2, and their failover address IP2.
The Node Agent probe relies upon the DAS for getting the status of the Node Agent. If DAS fails, there is no way to determine the status of the Node Agent. You need to ensure that the DAS is running at all times to know the status of the Node Agent.