In xfce, I can run Settings -> Display to change my preferred output monitor. What I haven't found an option for is to have it automatically adjust to a change in available outputs.
For example, if I'm using a DVI display, but undock my laptop, XFCE will not automatically realize that I no longer have a working display and change the output. Gnome did do this, though I'm not sure through what service. I'd like to have some way of making sure I always have at least one working output automatically.
SIDE NOTE: This is related to another question of mine, If I just use a window manager and not a desktop environment, how do I get automatic dock/undock resolution updates?, but is for xfce, not any generic window manager.