I find it quite bizarre that people are seriously speculating that Nikon, #2 in DSLR sales and profits with daylight in third place, is threatened with extinction by the second tier SLR systems of Konica-Minolta/Sony/Zeiss, Samsung/Pentax/Schneider or even Olympus/Panasonic/Leica.
the success of an SLR system depends greatly on factors like its lens selection, camera components like auto-focus and auto-exposure, accessory systems like flashes and so on. In these areas, both Canon and Nikon are solidly clear of the competition, notwithstanding even the the smaller SLR makers' new partnerships with old-guard German lens makers Schneider, Leica and Zeiss.
P. S. Nikon collaborates with Nikon on sensor designs for Nikon SLR's, not to mention providing Sony with the steppers that it needs to make those sensors. (Would Sony try to abandon Nikon and go to the other major stepper maker, Canon!?) To some extent, Nikon might be indirectly reselling some of its sensor technology for use in Pentax and Sony SLRs.
This is probably related to the exclusive period that Nikon seems to get on each new sensor model. It is for now not clear if the Sony A100 uses exactly the same sensor as the D200 or a lower cost version, stripped on the multi-channel read-out needed to reach 5fps, and perhaps lacking the ISO 100 and 125 capability (the A100 does 3fps and has minimum ISO speed of 160).
And as a variant on pom's ideas, Fuji is one of various alternative sensor making partners for Nikon; Fuji is already generating sales for Nikon lenses, accessories and the numerous Nikon components used in Fuji DSLR's.