The Federal Trade Commission (FTC) has the power to deny or undo a company merger, if it creates a monopoly that hurts the consumer. So your situation could potentially be struck down. However, I doubt it would be. As clear a monopoly as it is, I don't think that the FTC could claim it hurts the consumer.
A monopoly on a "need" such as transportation is dangerous. If the company skyrockets its prices, now you either have to spend lots of dollars getting to and fro, or lose your job and make no money and DIE!! Okay, I'm exaggerating but you get the point. Your ability to live is affected.
On the other hand, a monopoly on a want, like going to theme parks in Orlando, isn't dangerous. If Comcast owns them all and decides to skyrocket the prices / stop maintaining and adding attractions, then you can simply choose to vacation elsewhere. Or vacation not at all. Or go to Fun Spot. Eww! But your ability to live is not really affected.
I know you didn't ask for that long reply, but I find stuff like that interesting. And while I'm interested in seeing how the FTC would handle it, I don't want to ever know the answer.