I don't think it will be twenty-plus years (although they are almost certainly saving 'James Bond' as a title to re-launch the series in the event of a long, legally-instigated hiatus), but it will probably be around 2027. I tend to view the series as over, otherwise I'd spend half my life impatiently anticipating the next film.
Barbara Broccoli doesn't appear to have the enthusiasm or perhaps even the work ethic required for an on-going series. Her father had more tenacity in his eighties than she had in her forties. I'm not saying it's all her fault - the situation with distribution rights is clearly a headache, though perhaps not as much of one as the lengthy negotiations seem to suggest - but it will be interesting to see how swift the turnover will be when Greg Wilson or someone inevitably succeeds her.
The series has had some considerable gaps (1989-95 etc) and still returned with astonishing success, and that could well be a serious problem in the long-term. It has shown Eon that Bond can maintain its status regardless of how much time elapses between films.
My Top 10 Bonds: Octopussy, Goldeneye, From Russia With Love, Tomorrow Never Dies, Licence to Kill, For Your Eyes Only, The Living Daylights, Moonraker, Goldfinger and The Spy Who Loved Me.