He could have 100,000 bitcoins in his wallet and he will have trouble converting them to anything other than bitcoin because the NSA and every other intelligence agency is on him like fly on shit.
The second he tries to cash out an account at Mt.Gox , CampBX or any exchange for that matter it'll get seized. They would most likely let him sell his bitcoins but not withdraw, so at the end of the day he'll have neither bitcoins or dollars (or Euros, Yen, whatever).
He's going to have to find lawyers that accept bitcoin, food stores that accept bitcoin, etc... because he most likely won't be able to convert it to anything else. Technically doable... but boy he has his work cut out for him.
I do not understand why are we obligated to trade on online exchanges. For example if anyone come in my country to visit and wants to exchange bitcoins for cash he does not need to do that on online exchange, there are people that are willing to change crypto currency in fiat with reasonable fee and that is even faster than banks. My friend waited 2 weeks to get his money from mtgox. I am not saying that online exchanges are bad but they are slowed down or even restricted by banks. Whole point of crypto currency is to avoid banks and governments because I want control over my assets and I will not pay taxes 3 times for one thing.