Would doing <bind>D (note the casing) help? It will list all the currently attached sessions and allow you to remotely disconnect them. I use it when I forget to detach at home and I'm at work or vice versa.
I basically want an untouched session to go into a screensaver mode where it no longer controls the terminal size.
It's certainly not the end of the world to detach them, but I'd rather not. And detaching before I leave a session is just busywork.