I'm fiddling with a fic and a plot bunny for them. At the point I'm at, they just saw each other for the first time in sixty years, and then Jack bolted.

The plot bunny is that Jack and Estelle do manage to keep their promise - but only since Torchwood Three kept him under house arrest for a decade, and Jack escaped and by the time Torchwood caught up he'd joined the RAF and they left him alone because, hey, there's not going to be a Empire if the Germans conquer them and leave him be.