* If a cofounder, he's probably entitled to shares. As a cofounder, talking to the board or investors would fit the character (he /was/ a cofounder)
* If an employee, as employee was getting paid or equity. Upon termination, he would receive severance. I think the discussion about how many tickets, what percentage of the booth, etc isn't very different from a company firing an employee and discussing how much severance. For a company with no money, how to split the assets.
In general, as investor/board member, I would be shocked to know that an employee - who hasn't signed an IP license agreement - is walking away, without signing an IP license agreement, making the entire IP asset of the company a potential legal liability. As board member, I'd have advised the CEO to QUICKLY settle this IP dispute, to give in on everything requested (booth, tickets, etc) - BUT - to receive a signed paper claiming full ownership of the project. Booth and tickets can easily be replaced. A startup whose IP ownership is unclear will be a dealbreaker for any investments during ANY due diligence process.