Thanks for the prompt. My sense is that the criteria for evaluating whether an employee is integral or not varies based on the company (and technology) being acquired. Every case is different… but generally knowledge of products (IP), key sales relationships, and leadership competency/potential are good places to start from an evaluation standpoint. It is inevitable that some employees will leave, so this is why it is important to identify and prioritize plans to retain key employees from the acquired company. These plans should be developed during the merger integration planning process.
All the best.