WI Edward VIII declares his abdication and George VI-s accession to have been valid all along - BUT offers to accept the throne again from a "free parliament"?
Compare Dutch conquest of England in 1688. England was conquered by regular Dutch army hired and authorized by the States-General of the Republic of United Provinces. Then a Convention Parliament called by the occupying forces and elected during Dutch military occupation "deemed" James II to "have abdicated" by evacuating the realm - and offered the throne to Williamandmary, who just happened to be the Captain-General of the occupation army. (Scotch parliament could not call actions of James II "abdication" because he was not in Scotland to begin with - they were simply willing to call the throne forfeit for misgovernment.)
Note that James II did, in fact, fight for his loyal realm of Ireland all that time.
If Germans manage to conquer Great Britain and George VI chose to flee to Canada, could they call George VI abdicated or deposed despite his holding out in Canada, by analogy with removing James II while holding out in Ireland?
Would elections of Parliament be held in occupied Great Britain where much of the old political elite would have evacuated to Canada? Elections were, in fact, overdue - the Parliament elected in 1935 chose to sit till 1945 without calling a general election.
Who would have fled to Canada, who´d be held in prison by the occupants, who would stand for election but lose at the polls, and who would take seats in Occupation Parliament?
What would James II have done to the persons of Williamandmary when captured alive in Jacobite restoration? And what would James III have done to Anne? George I? George II?