Nisei is FAR from dead. The overall Kinnikuman franchise is still incredibly popular in Japan, even if Nisei has never quite reached the popularity of the original series. Think of the original Star Wars trilogy compared to the prequels... Lucas can do whatever he wants because of the success of the original three films. Same with Yudetamago.
The original Kinnikuman series merchandising and brand is still "A List" in Japan when it comes to collaborations and co-branding. That kind of nostalgia and popularity allows Nisei to continue on (despite comic sales) because it is all about merchandising and advertising revenue now.
Nisei sells online Weekly Playboy Japan mobile subscriptions, gravure movies and pic downloads from Shueisha's website and mobile apps. Gravure sells, and Nisei helps to sell a lot of it... seriously
