Last night on MSNBC, John Hofmeister, former Shell president (American branch, not Royal Dutch Shell head), said that the top kill being used is a "long shot."
We can hope.

Ed T., thanks for the link to the Scientific American article.
At the close, it said that the process could take a long time. Even a year may be too long since lost not only is a breeding season but also a migration season.
These microbial helpers will help restore the faunal and floral chains, but some wildlife, such as the turtles, probably will be premanently decimated.