Maguire says "This might be a good place to stop - I am not tied contractually to any more Spider-Man movies. I am not completely closed to the idea of another one if it made sense but I would say the odds were in favor of this being the last one".
I'm sure that Sony isn't thinking about the end of the Spider-man movies. But it will be hard to replace Maguire, who fits Peter Parker to a "T",if he decides not to come back for a possible fourth movie.
Both Maguire and Dunst, who have three film contracts, have expressed mixed desire to return to the franchise now that they've finished working on the three films.