As you’ve rightly pointed out, the key challenge is that Business as Usual and PMI are often competing for the same employees, so leaders need to monitor both sets of indicators in parallel.
From a BAU perspective, I would closely monitor revenue trends, customer retention and service levels. On the customer side, deterioration in key customer journey metrics, such as delays in onboarding or delivery/installation, should be treated as a warning sign that integration activity is starting to create disruption.
Rather than slow the integration process down, the key for leaders should be to reprioritise:
1) Protect the most critical and high-value customer journeys
2) Defer lower-priority integration activities where necessary
3) Add temporary capacity to stretched functions
4) Escalate resource conflicts quickly through the IMO
This highlights the need for clear KPIs to be defined and established for BAU and PMI pre-close. If both are measured and monitored consistently, leadership can intervene early and adjust sequencing without losing overall integration momentum.