If he’s on contract, it won’t be renewed and they might just go ahead and terminate anyhow — giving one month’s notice as is standard in most Japanese contracts.
As someone who stayed and did my job (actually jobs) I find it extremely difficult to sympathize with this guy. Bailing on your coworkers and leaving them to not only their jobs but yours, too?
Not something anyone in his office is going to forgive or forget anytime soon.
And if it bothers him, I suggest he take his fluent Japanese speaking ability back to some safe school in wherever he came from and get a teaching job.