That's what vesting is for. He's clearly not entitled to 20% of the sale price, but these people are behaving like contemptible assholes and he should get something.
He should figure out what he'd have if there were a 4-year vesting schedule in place and settle for that. He would get 1/4 of his partner's take if he had stayed for the entire vesting period, so if he was there for exactly 1 year, he should get 1/16 of whatever his partner got.
Here's the reality he faces, though. He's up against sleazebags who are going to try to make sure he gets $0.00 and he's going to have to fight to get anything. He needs a good lawyer. We can't help him.
He should figure out what he'd have if there were a 4-year vesting schedule in place and settle for that. He would get 1/4 of his partner's take if he had stayed for the entire vesting period, so if he was there for exactly 1 year, he should get 1/16 of whatever his partner got.
Here's the reality he faces, though. He's up against sleazebags who are going to try to make sure he gets $0.00 and he's going to have to fight to get anything. He needs a good lawyer. We can't help him.