Marketing theory always insists that a first-class brand's potential is nearly endless: no one in the world of publishing, consequently, will have been in the least surprised to learn that JK Rowling has not bidden farewell – or not quite bidden farewell – to Harry Potter. According to an interview with Oprah Winfrey, the creator of Hogwarts, the Death Eaters and Quidditch, while not actively planning any sequels to her seven-volume sequence, is not ruling them out. Harry, Ron, Hermione and their chums are still roving effortlessly through her dreams, and it would be wrong to bring the drawbridge definitively down on the prospect of their reappearance.
Ecstatic as millions of Potter fans will no doubt wax over the remote possibility of fresh adventures, it is worth pointing out some of the dangers that lie in wait for writers bent on reanimating a series of characters long since thought dead. Danger number one lies in the creative imagination's habit of refusing to reignite. The late Simon Raven, for example, author of the Alms For Oblivion series (10 vols, 1964-1976), was later pressed to reassemble his cast, and their heirs, for a further seven instalments. The result was a disaster, of which Raven remarked, "One would wake up in the morning and think, 'How can I go on with this? Please God, let me win a football pool and disappear out of this appalling world and this appalling undertaking for ever...'." Sadly, the Littlewoods' cheque failed to arrive, and the results – First Born of Egypt (seven vols, 1984-1992) – can be found mouldering on many a library shelf.
And to creative stasis can be added the fact that most fictional franchises belong to a particular time and social environment, from which their characters must, if they are to retain any sense of conviction, eventually allow themselves to be superannuated. Thirty years ago, as a succession of Ian Fleming surrogates was employed to extend the James Bond series, pundits used to wonder whether "M", references to whose Edwardian boyhood decorate the early volumes, shouldn't now be enjoying a dignified retirement. Martin Amis, too, has written of his attempts to redeploy some of the characters from his early work, only to give up in the certainty that their sell-by date had already been exceeded.
The same principle applies to TV sitcoms, which nearly always falter when they march out of one historical world into another. I can remember Stephen Fry once telling me, in excruciatingly funny detail, about the efforts that were made, two decades ago, to develop a fifth series of Blackadder. This was either to have been set in the distant future and called Spaceadder, or to have followed the misadventures of a rock band in the hippie era, with Tony Robinson upgraded from Baldrick, dogsbody to the great and good, to "Bald Rick", the band's put-upon roadie. Even this, though, never left the producer's desk, on the grounds that most of the humour of the existing series relied on the incongruity of young men impersonating old men against a mock-historical backdrop. The near present – or some phantasmal realm beyond it – presented difficulties that no amount of creative pizzazz could overcome.
Going back to Ms Rowling, continuing the lives of Harry, Ron and Hermione offers several well-nigh insuperable challenges. Even if she starts writing volume eight tomorrow, Daniel Radcliffe and his co-stars will be pushing 30 by the time it hits the big screen, raising the possibility of a kind of Friends-on-broomsticks. An alternative would be to wait until everybody's children have grown up and set them battling against some incubus-descendant of Voldemort long concealed in the Hogwarts cellars. All the evidence suggests, though, that Ms Rowling should stick to the example of Anthony Powell, who, having killed off Widmerpool at the end of A Dance to the Music of Time (12 vols, 1951-1975), stoutly resisted fan pressure to carry on the series. In art, as in life, you can have too much of a good thing.