If its not on the surface to be visually seen now that the well is almost capped, anyone with brain one knows some 20 Exon Validizes of oil just did not disappear.
On the plus side, the Gulf of Mexico has far more water and coast line than Prince William sound, the temperatures are far hotter so natural biologic oil breakdown processes proceed at exponentially faster rates, but still, no one knows how long and how badly the Gulf coast is damaged, or how long it will take to clean up. Or how expensive the process will be.
As for me, since I don't know and don't claim to know, I think we are going to have to let time and experience answer those questions. All else is waste of time speculation.
But maybe Spidey will be so correct in part one, and so wrong in part two. We could get massive blooms called a red tide, that end up killing all fish life in a 500 mile diameter or bigger.
http://www.whoi.edu/redtide/