A company that talks about bonuses of that size with no legal contract didn't care enough about it to start with.
The developer will pay with his reputation. Any employer who knows what happened will never fully trust him, except after a long working relationship.
Miso will pay by losing potential hires.
Each side loses more than 10,000 dollars worth. Justin's professional rep is worth a lot more than 10k, Miso's hiring future is worth more than one bonus. They should have worked this out in private.
They couldn't, and they both lost.