Japan is a huge producer of tech, from video games, to tvs etc. The Japanese excel at producing and packaging tech. It's not likely people aren't going to want to keep buying new technology every few years, but it's a good idea not to put all your eggs in one basket.
I am assuming that this question was asked by someone who does not actually live in Japan. The economy of Japan is already quite diversified. While it appears that technology is its primary export, it's also a leader in transport (trains, buses, cars) production, and also in agriculture and food.
Without a doubt, the economy of Japan needs to focus upon more than just technology companies. Tech companies can't prop up the country's economy for the next fifty years without extra help. More industries need to be explored and mastered in Japan. Otherwise, the country will soon see some decline.
The economy of Japan only appears technological in nature to outsiders, because that's what they primarily export to the rest of the world. Of course we're forgetting about the auto industry, but perhaps that could be argued as technology as well. But there's also manufacturing, medical, agricultural and textile concerns in Japan as well. The nation's industry is quite diverse.
The economy of Japan should not diversify beyond technological companies. This is because of the fact that they are already the masters of their craft. Technology is also the most important aspect of the human race's future and to have a domination on that area will only serve Japan well.