If that's the case, I'd all but force him to go. He made a commitment, didn't keep it, and needs to learn to face the consequences.

If he just absolutely hates piano, ask him what other talent he'd like to develop, because sitting at home and playing video games all day isn't an option.

Or he might just be in a slump, which all musicians go through. He needs to know that it can be a drag sometimes, but that if he sticks to it, gives some effort, that he can get really good.