Antony Johnston, the writer of the Alex Rider graphic novel adaptations Stormbreaker and Point Blanc, has contacted me to say there are more Rider comics in the future. This is great news, as there isn't yet another title listed on Amazon. But Johnston has finished adapting Anthony Horowitz's third novel in the series, Skeleton Key, and expects to start work on the fourth, Eagle Strike, "sometime this year." Presumably Skeleton Key will be out around Christmas, following the pattern of the first two graphic novels.
Johnston also wanted to correct my earlier story and assure readers that despite the incorrect image on Amazon.co.uk, his adaptation of Point Blanc did indeed retain the pun of the original British title in the U.K., and was only changed to "Point Blank" in the United States, reflecting that change in the original novel.
As long as the graphic novels continue to sell (and apparently they're selling very well), Johnston is confident that the series will continue. Hopefully that means we'll get all of Horowitz's Rider books in comics form eventually! I'd love to see those supplemented by some original Alex Rider comic stories (ideally written by Johnston or Horowitz), but Johnston says there are currently no plans for anything like that.