Most deals are modelled on synergies; most integrations are lost on people. Having supported large-scale HR integration, the first 100 days set the tone for everything that follows.
Three priorities dominate: retaining the talent the deal actually depends on, harmonising terms and governance with defensible logic, and communicating with a discipline that assumes every message will be forwarded.
Speed matters, but perceived fairness matters more. Employees forgive difficult decisions far more readily than opaque ones.