There was the Fleming inspired film "The Poppy Is Also A Flower" (aka "Danger Grows Wild") about the drugs trade in Afghanistan. It was directed by Terence Young, starred Terence Stamp as a drug enforcement officer, and though a work of fiction was made at the behest of the United Nations to warn of the dangers of the drugs trade. Might that have been, originally, the basis for a Bond novel? We know that the upcoming "Trigger Mortis" novel is based on unused Ian Fleming material as well. Who knows what other plot ideas he might have had lying around.
But would Mr Fleming have wanted to carry on with Bond after You Only Live Twice and The Man With The Golden Gun? Who knows? He had every financial incentive to do so thanks to the success of the Bond films, and I'm sure Messrs. Salzman and Broccoli would have been delighted at the prospect of further Bond adventures to film.
However, had the creative well run dry regarding Bond? He did seem to be tiring of the character. Fleming started branching out into other types of writing for publication as books - travel writing, children's stories and so on. Maybe he would have taken a break from Bond, tried different projects, then a few years later returned to 007 - and that would have been a publishing event!
As for the type of Bond novels Ian Fleming might have continued with - his stories often reflected what he had read about in his youth or experienced in his various careers. Could his James Bond have adapted to the changing times of the late 1960s and early 1970s - or beyond if Fleming's health had held up?
In the end it was his state of health, the strain of the Thunderball plagiarism court case, and the pressure of trying to keep Bond going that did for him. We'll never know what might have happened were it not for these factors. As John Pearson put it in his biography of the author; "James Bond had finally destroyed his only flesh-and -blood victim."