Sure, but 800k out of 120m people is nowhere near affecting the senior citizens of the future. Time will tell if it's a stabilizing change that will oscillate around some baseline, or if it will continue to drastically decline.

And even if a drastic decline is the future we're looking at, there is no shortage of immigrants who are willing to take menial jobs for low pay. As far as I know Japan hasn't been an inviting immigration destination so far. There are policy changes to make that could easily inject some population to the country.