You could use CSS to hide the ‘Members’ link in the chat info. But, a user could reveal that if they enable safe mode with themes OFF but plugins ON.
So perhaps the best way is to create a plugin to remove that page/empty backend but overrides the frontend. That way, disabling plugin customizations would also disable chat entirely, so users can’t get the route. I think. I’m on my phone now but I’ll try this out when I’m back on my computer.
Sorry for the technical solution, but no Discourse-native solution comes to mind.