I love both of these characters too much to want either one of them dead, but in the end, if there came a decision, I think it would be this.
Changing Places
It had been spur of the moment, but neither involved would change the decision once it was made.
He smiled at his granddaughter, and she smiled back, nodding.
"Knew you'd rather it this way, gramps."
Nodding, Wilf grimaced in pain. "Ah, my girl. My little general. You keep on fighting, you hear! Keep on...keep on going for me."
Donna nodded and kept smiling, even as the tears started. "Sure, gramps. Anything you want."
After that, everything went silent but the noise in his head, but Wilf knew he had done the right thing.
He had exchanged his life for Donna's. He had lived a long, full and exciting life. Hers had barely even really begun.
Time to let her live.