What became of the Chappaqua Mountain Institute in Valhalla?

Back in business with the first update in seven months, version 8.3 of the list (pdf) includes these items:

• The “Bettis Bungalow Hospital” in Chappaqua has been identified as a hospital or infirmary building at the Chappaqua Mountain Institute in Valhalla, N.Y., directed by Charles R. Blenis. Do you know what became of the Institute after World War I?
• The modest two-level storefront addition at 55 West 28th (Street View) has been identified as a Hugh Lamb project of 1902.
• Frederic A. Angell’s late-1880s house in Montclair, N.J. has been identified as a Lamb & Rich project.
• The standing “Cliffside Chapel” or St. James’s Episcopal Church has been identified as a Lamb & Wheeler project (it is typically attributed to Lamb & Rich).
• New information on the unbuilt L&W building at 37, 39 Greene Street has been included; it turns out that the client was Hugh Lamb’s neighbor and future father-in-law.
• Corrections have been made to 825 Broadway, the project for Bernhard Cohen, George Lowther’s Riverside (Conn.) address, and the Colgate Delta Kappa Epsilon House (still standing at its prominent location: Street View).