Some last, some don't. My in laws have a stash of slides, 30-50 years old. Some Ektachromes are ok, most are faded beyond recognition. Kodachromes look like new.Although rockland's couplers might be completely crap compared to Kodak's, I assume they offer fairly long-lasting dyes. People have been using this product on black and white prints, so I assume it's not that bad and will last a decade or two at least. The old films and whatnot did not have very good couplers, yet they still last quite some time, albeit with some fading.
@AgX: color film products changed a lot, even when the process itself didn't. Therefore color developer itself may be important, but choice of coupler definitely affects longevity of final product, too.