Legal Question in Employment Law in California

Only if vacation or any other benefits are promised/guaranteed by the company policies [written or 'common'], or in an offer letter or contract with an employee, and only if they are payable upon termination if not 'used', would the company be obligated to pay. If he can't prove both those issues, he can't win a claim for them. It is up to you to decide whether to honor your 'promise' to him and pay, or deny.

Every company should have a policy manual and employee handbook clearly describing this and all the other issues that make up personnel and operating policies and rules for the company. It is very poor business management to operate without all such issued decided upon by the company, and put in writing so there is no question or dispute after the fact. Anything less will get you in similar legal difficulties, costing you attorney fees to resolve that far exceed the cost of doing it right to start with.