Video window left on the secondary monitor

[Ico-man]

"Otherwise another option can be (not an option, but hardcoded to always be performed) to place the Movie Window at 0,0 when that window is entirely out of sight"

This is already implemented in BS.Player, as long as you have Single display enabled.
If you are watching movie on a second display under Dualview mode, and then want to move the movie window to primary window, all you need to do is change display mode to Single display, and BS.Player will detect that movie window is out of sight and will display it on primary display.
Tested.

If you want to keep using Dualview all the time(i.e. do not want to change display modes everytime you watch different display), but don't want to drag movie window from primary to secondary and back all the time, just check the "Don't remember movie window position". BS.Player will then always display played movie in primary display.

:)