A roadmap and a 100-day plan both leadership teams own, so the business keeps running while the integration moves.
Every integration is full of surprises. To stay agile, the team needs a clear destination and a solid plan to get there. Then, when things go off the rails, it can react, and often get ahead of the problem.
The way to avoid overwhelming the organisation is to build the roadmap with both leadership teams in the same room, and to develop the 100-day plan from it. Planning together is what lets the joint business agree priorities, run day-to-day operations and still have time to drive the integration.