If we split into these two logical sites, will the PAM service continue to operate on the remaining site if one of them stops?
Or will the PAM service stop unless we restart one of the sites and return it to the multi-cluster?
If split into two sites... one node becomes the primary site and the other is a secondary site.
If the secondary site node fails, the primary site is not impacted and can continue to service user sessions.
If the primary site node fails, then the entire cluster halts until either the primary site is restored OR the secondary site is manually promoted as the new primary site.
This is actually more resilient than a two node primary site, which will halt if either node fails and will require manual intervention to recover.
The primary disadvantage of splitting the nodes is that the built in load balancer will no longer work. Users will need to manually select which node to log into, or an external load balancer would need to be deployed.
Keep in mind that the optimal solution would be to simply have three nodes in the primary site. Additional nodes are relatively inexpensive, and a three node primary site is resilient against any single node failing.