It would be easy. Just leave him there, just do nothing.
I wasn't like it mattered much, one old man, near the end of his life anyway, who would never do anything of any great importance, and had no effect on the time flow. His lose would be absorbed by the time flow, compensated for and wouldn't matter.
It was easy. It was simple. He could do it, just turn and walk away. He could live.
Except or the part where he really couldn't.
Because this was Wilf, who was foolish, and kind and loved Donna so very much. Because this man, this sweet, stupid ridiculous man had gotten in this mess to help someone who wouldn't even remember his face. Because Wilf was an innocent, and loved him as his own father never had.
So he was going to die. The Doctor would continue, but he'd liked being this way, it had been fun.
But he couldn't let Wilf die, couldn't live with the guilt if he did, so he surrendered to the inevitable, and walked to his death without flinching.
"Come on; let's get you out of there."