Just to clarify about taking the $500K rather than even guaranteed additional $5M ($50M vs. $45M) years later...

$500K is an immediate big quality of life boost for most people.

For example: a condo/house downpayment, which lets you move out of cruddy ramen apartment, to routinely get a good night's sleep. And/or that relieves some of the various other startup salary level money stresses on your family.

I think this can also be aligned with the goals of the startup. You don't want people so "hungry" that the stress is hurting their health and their home lives. You want them motivated by the mission, the work, the environment, and the possible big liquidity windfall in the future -- but not by desperation.