i don't think that there should be any problem when he travels back to US after sometime.. he can enter US anytime but at the port of entry they will ask your friend the purpose for traveling back US.. and he should be able to answers back why he applied for the visa extension when he was here. for that he can say that he wanted to travel weat coast if he was in east coast or vice versa.. but the purpose of the visit next time he enters the US must be clear.. that's just in case.. but as he is ready to leave the country after he was denied the extension there should not be much problem for the next time.. but may sure you can answer them back with out any doubt.. i hope other then put some more input in this regards.. thanks..