I know it has been a couple of months but I did not any posts about Elana Verdugo's on May 27th, she appeared The Sky Dragon.
There are not many if any actors left living from Chan films. R.I.P. Elena
There was brief mention of this topic on Dr. Cream's "Charlie Chan Message Board". There was very little discussion, but no one posted any information about any other adult-age Chan cast member who is still alive.
Yes, Elena Verdugo was the last remaining actress/Actor of note from the Chan series. As you mention, there are probably a few of the child actors who portrayed Chan siblings. Hawaii Steve had contact with the gentleman who appeared as the baby slurping the noodles in "Charlie Chan in Honolulu," but, alas, I believe he, being in poor health, has passed away.
About eight or ten years ago I attended a "Hollywood Show" celebrity event in Burbank at which both Elena Verdugo and Noel Neill were both in attendance. I had both sign a lobby card from "The Sky Dragon." Noel Neill had no recollections to share about the Chan film, and Miss Verdugo had scant information to share as well. This was probably due to the fast-paced production norm at Monogram Pictures where actors would do their work and leave, basically. Verdugo did have nice things to say about Roland Winters with whom she had worked on the TV comedy "Meet Millie."
Sadly, time moves along, often, seemingly, with the speed of those Monogram productions...