In response to Vera, I would say "No, he doesn't owe anything".

He's an employee, plain and simple. He got paid to fulfill a service. He did that service well. He then wants to fulfill services elsewhere and decided to do so. Tasks and services were completed, what more can you really ask?

I'm in the same boat. After over a decade working at the same place, I feel its my time to go as well (after all, I want to build a business instead of just be an employee). I know that I'm probably the guy in the company's plans, but I had to look at it this way - You're always needed wherever you go if you do your job as well as you can.