Falling back on Fred would be more of an emotion based response since the only argument for him would be "the devil you know." The idea that we would even start a cold goalie coming off injury with question marks to his mental game over a guy currently on a roll doesn't make a lot of sense when talking about transitioning from Game 56 to Game 1.
Re: Campbell, he's a guy with no track record whatsoever, so seeing him bounce back is trying to get an understanding of how he plays over a longer sample size. The fact that he can bounce back is a sign he can work through adversity.
Not saying we couldn't ever go back to Fred if Jack struggles, but the idea that the net belongs to him just because doesn't sound like a compelling argument.