Let's back up a bit. In graduate school, a C is considered failing, and students typically are expected to keep up a B average. When I was a student, we were expected to keep up a B average every semester as well as cumulatively. Two consecutive semesters where we didn't, and we were out. So an F is a very, very strong statement. It's a grade that is so low that it jeopardizes your chances of staying in the program, as it takes 3 A's to counterbalance. The professor knows this, and if he gives an F anyway, it's saying a lot. It also means the rest of the department knows this and is either on board, or that the professor feels so strongly about this that he's willing to cross his colleagues to make this statement.
With an F, I'd be more focused on graduating than on post-graduation prospects.