An organization wants to run on-premises instant messaging (IM), and resilience is important because this...

The logs don't directly address this question, but based on best practices for on-premises IM and Presence with Cisco UCM:

Disaster recovery and failover are crucial for business-critical applications like IM.

Deploying two Cisco IMP servers (one publisher, one subscriber) per location provides redundancy within each location's Cisco UCM cluster.

While Cisco UCM can potentially handle some IM functionality without a separate IM and Presence server in newer versions, Cisco IMP offers a more robust solution with features like disaster recovery.