Can I collapse content spread across two displays to a unique space for each display when the 2nd display is removed?
I have not tried that specifically, but after trying out pretty-much every window-position-remembering app out there, I found that only Stay actually did what I wanted.

It lets one save the window configuration for each display configuration, and seems to be Spaces-aware.

I have nothing to do with them, but thought they provided something useful.