Yeah I think it was kind of obvious that scene (as fun as it was) was a late addition. I'd wager that Krennic didn't originally die on Scarif too, but originally got back to the Death Star in one piece, where Vader was waiting for him.
Thanks for posting a link to the video; I had missed this.
I now understand the start of ANH a lot better. After the crawl, Tantive IV is shown in a shoot-out with the Imperial cops. Therefore, the diplomatic immunity argument holds no weight.
Maybe Tantive and Vader's Star Destroyer have been chasing and blasting one another since Scarif?