Discontinued cards are not immune to changes.
You are, of course, 100% correct. However, the last Ritz change was an increased free-night certifivate to 85K, while the annual fee remained at $450.00.
I am fully expecting the annual fee may be increased, at some point, and am surprised it hasn't already, but I would hope that Chase would add some additional benefits to justify the increase.
There is always a chance they could drop the card entirely, and force a product change, but I would only expect that if Chase and Marriott parted ways.
I just think at this moment, the Ritz may represent a value proposition to dissatisfied CSR holders.