I'll point out that I read Steven Brust's Vlad Taltos series, which started in 1983, is projected to run to 19 books with 17 done. Brust is 70, but he appears to be in reasonable shape, and the books have been pretty regular of late, so it looks like he'll finish.

I also read the War Against the Chtorr series by David Gerrold. That also started in 1983, but the last published book, the 4th of 7, came out in 1993. Gerrold being 81, despite his claims for almost a decade that books 5 and 6 are near completion, I am confident I will not see the end of the series written by him :-(

> the books have been pretty regular of late, so it looks like he'll finish.

That was true for GRRM twenty years ago, but not today.