If a leaving employee is so important, you should ask yourself "Am I really 100x-1000x (whatever ratio your equity is to their equity) more important than this employee?"
Well, given that the company literally wouldn't exist without a founder, the answer to your question can only ever be 'yes'.
I can make you a company in an hour for a few hundred bucks. How many do you want?
Creating a company is not hard; building it is, but employees contribute to that as well.