Key takeaway
If a handover needs a two-hour brain dump call, the project's real record was living in someone's head.
A project manager or key contributor leaving mid-project is a normal, unremarkable event: people change roles, move companies, go on leave. What is not normal, but is depressingly common, is how much of the project's real state disappears with them, not because anyone hid anything, but because most of what actually mattered, why a decision was made, which stakeholder is difficult about which topic, which risk everyone quietly agreed to watch, was never written down anywhere a successor could find it.
The handover call is a symptom, not a solution
Every organization has some version of the two-hour handover call, where the departing person tries to transfer everything in their head before their last day. It is better than nothing, but it is a bad way to transfer knowledge: it depends entirely on what the departing person happens to remember to mention, under time pressure, on their way out the door. Anything they forget simply does not get handed over, and the successor has no way to know what they do not know.
Making the record the thing that gets handed over
The realistic fix is not a better handover meeting, it is a project record thorough enough that the handover meeting is a formality rather than the only transfer mechanism. Scope, milestones, risks with their history, and a decision or two logged in context as they happen, not reconstructed from memory afterward, mean a successor can actually read their way into the project rather than depending on one person's memory and goodwill on their way out.