If an employee leaves prior to a liquidity event they have to exercise their vested options, which involves spending their own money. The employee who stays on does not have to take any such financial risk. I don't know what problem you are really trying to solve. You mention employee retention at the end, but the rest of the piece makes it sound like you're really trying to eliminate some sort of hypothetical sour grapes. I don't think the latter is really worth solving, and the former has proven to be mostly unsolvable.