Why do Carine and her parents wish they'd let Chris bring Buck with him?

From the text:

“Chris was crazy about Buck,” Carine says. “That summer he disappeared he’d wanted to take Buck with him. After he graduated from Emory, he asked Mom and Dad if he could come get Buck, but they said no, because Buckley had just been hit by a car and was still recovering. Now, of course, they second-guess the decision, even though Buck was really badly hurt; the vet said he’d never walk again after that accident. My parents can’t help wondering—and I admit that I can’t, either—how things might have turned out different if Chris had taken Buck with him. Chris didn’t think twice about risking his own life, but he never would have put Buckley in any kind of danger. There’s no way he would have taken the same kind of chances if Buck had been with him.”