Denslow returned to the character in 1906, in hopes of creating a story that could be turned into a Broadway extravaganza. The result was a rather uninspired book, written in conjunction with Dudley Bragdon.
The character was popular and inspired a variety of merchandise such as pinbacks, cigars, and a toy bank. The bank seems to have been reproduced recently, with an example I picked up shown below on the left. On the right is an advertising cut for the original bank.
While the character is largely forgotten today, an animated cartoon based on the book was created in the 1960's as a pilot for a projected series. The project never took off, but clearly someone had remembered Billy fondly!