Why drag Sadie along?
Why did Jake drag Sadie to the TSBD at all? History does not record she was there, or had any role in the events. What did Jake want Sadie to do there? It was indeed a danger to her life, so if he loved her, he should not have brought her there.
Also, the bum keeps saying nothing will ever change, so Jake trying to change anything would not work, and JFK will always die, and so he cannot save Sadie too.
Well, about JFK he was right, he did die at the end after the reset, however, Sadie did live... so there, proven wrong!