The strongest indication that there will be no future replacement for the F100, is that the replacement was launched last year. It's called the F6, and is obviously positioned to replace both the F100 and the F5. The size being close to the F100 until you fit the vertical grip, which actually makes it bigger than the F5, and the technology being a step up from both cameras.
While many of Nikon's customers, and probably other SLR users around the world, see a need for, or just the pleasure of using, a top spec film SLR, the market isn't big enough for two cameras. The fact that it's more expensive than the F100 isn't too important. The enthusiasts and the professionals who use these cameras will mostly buy lenses for many times the price of the body anyway, unless there are some purists out there who will only use it with a 50mm 1.4 (hmmmm... I think I'm a candidate for a concept like that, but an FM3A with a 1.2 would be even more purist, wouldn't it?)
A much more interesting question question is if there will be an F7 in 5-10 years. It sounds like a silly idea, but with KM, Contax and Pentax leaving the field, and Leica on very shaky feet, there really isn't much competition. Having the 35mm pro/enthusiast market more or less for themselves, except for a couple of Canon EOS1 customers, may be a good excuse to make another pro film-body based on the next generation pro-DSLR. Maybe not so much for the profit in it, as for the status it will give Niko n among its followers. It's like walking to the South Pole. It isn't very useful, but people will talk about you.
I agree with Larry about a used F5. Unless you think it's too big, it will last a lifetime. If you want the F100 replacement, buy the F6.