Suspend the machine instead? The external monitors will go to sleep when they lose the signal.
I don't know how you expect that machine to know that you're only disabling that monitor temporarily and you expect it to restore your windows at some future time when it reconnects.
If you plug in a new monitor, should windows jump onto it spontaneously?
I do the same, either my Dock, my Laptop or my screens, or all together give some weird issues where the screens turn on every 5 minutes and go to sleep.
And searching for 'Dock screen wakes up during sleep' just floods <search engine> with 'screen does not wake up after sleep'. And with <search engine>'s removal of respecting + and -, I am not sure I'll ever find a solution...
I don't know how you expect that machine to know that you're only disabling that monitor temporarily and you expect it to restore your windows at some future time when it reconnects.
If you plug in a new monitor, should windows jump onto it spontaneously?