No rematch clause - cause Hamed was over-confident. Plus - I doubt if he wanted to get his ass kicked like that again anyway. Barrerra wasn't probably interested in giving him one - because of how disrespectful he was. Similar to the situation between Hopkins and Calzaghe.
Because Barrera scraped him so bad the people were not interested it watching that type of abuse again
9/11 WOULD have affected his career if he would have continued fighting, he sure as hell wouldn't have been able to do that crazy stare and the 'allahu akbar' thing anymore. Not if he wanted to leave the venue in one piece.
because he would have prob took a worse beating barrera was walking through him in the last 2 rounds with ease he would have done this earlier in a rematch and prob stoped him