You assume you can buy happiness. Person A is not objectively better off, they're financially better off. Happiness isn't determined solely by bank balance.

If what made him tick was a sense of purpose, of seeing the company he founded continue to grow there aren't many options apart from go back to the company, found a new one, or ??? Maybe option 2 is too much work, and without the carrot of a big payoff he'd lack the drive.

You'd happily trade places because you believe money buys happiness. This person has learnt it does not.