It will ultimately depend on how well, the 3DS performs.
If it has at less then half of the success that the DS, then Nintendo bouncing from portables is a real possibility. But if it has at least half, Nintendo will be in the portable hardware market for at least another 15 short of a collapse on the console front.
For years, the NES and SNES supported the GB system until Pokemon became a new religion in Japan and then around the world. Then surprisingly the roles were reversed where the GB (or GBA really) was supporting the GC. Right now, Nintendo has been playing it safe by taking risks with input in the DS and Wii, without going overboard on their specs and they have made enough money to probably support themselves for at least another 15 years if at least the console or portable hardware and obviously software continue to sell enough.
