I pretty much agree with the above.
Internet relationships are tough. First, because people say things that they wouldn't normally say face to face. Second, because it's so easy to switch on or off a relationship. Think about your relationship with this person otherwise. Are there positive things you like about being connected with him? Balance it out-- is his refusal to apologize and to say something inappropriate in the heat of the moment worth blocking out the positive things? Also think about what benefit you might be offering him, and put that in the mix.
Typically, I have found that unless a person continues to be obnoxious over a period of time, it isn't worth cutting off a relationship. And then, you never know, he may wake up today and regret what he said, and he needs the opportunity to make it up to you. Whether that be an apology or another way of restoring the relationship.