Succession planning works best as a regular leadership conversation, not an emergency response to a resignation. Start by naming the roles your organization could not afford to leave vacant for long. For each role, document the key decisions, relationships, and skills the next leader would need.
Look at the people already on your team. Who could take on more responsibility now? Who might be ready after a stretch assignment, mentoring, or experience in another part of the organization? Be specific about the gap between current ability and the work the role requires. A name on a chart is not a development plan.
Review the plan at least once a year and whenever the business changes. Give potential successors meaningful opportunities to learn, while keeping an external search option open when the skills you need are not yet available internally. The goal is continuity and a stronger bench, not a promise of a particular job to one person.