The momentum can't be stopped for C/B even with a fall, albeit not on an element, so it wasn't very costly. They can't afford a similar mistake at Worlds, but I expect this to be a fluke
Historically, Chock & Bates's mistakes most often come when they are the ones expected to win. I would say that winning U.S. Nationals put that pressure squarely back on their shoulders prior to 4CCs.
Pretty much all the top 4 ranked teams heading into the event dealt with one of their usual demons under pressure:
G&P got their typical level 2 on the pattern and wobbled through a set of twizzles.
C&B splatted while the door was wide open for a win.
Zach missed the twizzles.
And Hawayek & Baker had another random splat under major-international pressure (this would be the third season in a row if you count the choreo slide last season--not that I, as a fan of one of their uber-matrix domestic competitors, would be counting or anything

).
Here's hoping everyone got these things out of their system prior to Worlds.
(I interrupt this negative-Nancy account of what happens to high-ranked teams under pressure to say

to Wang & Liu for a great competition at an opportune moment!)
I do think Guignard & Fabbri have a shot at the final flight at Worlds. They brought in the level 4 pattern at Euros, and if you can bring in level 4 there with that tech panel, you have a shot at it at Worlds. G&F cannot compete with the speed of the top teams. This, combined with G&P skating at home, sets G&F at a disadvantage generally.
I think the Montreal crowd is going to stand up for Gilles & Poirier after they skate anything, but especially after the FD where it will be treated like a hallowed & revered event. (This is an educated theory as I was at SC this year, and also I remember how loud the crowd was for the Shibs skating at the Boston Worlds). I also expect that G&P will get a level 2 on the pattern unless the caller or AT is Canadian or Higashino (neither of which seems likely as W&P were top 5 last year and Higashino called last season), though as
@VGThuy says, G&P do sometimes pull that level 2 up at the very last event of the year.
Yes, this is another problem with the judging system. The GOE for choreographic elements isn't factored to the value of the element so the choreographic elements are disproportionately valued in comparison to their difficulty. In the singles events, GOE is factored to element value and ice dance should do that, too.
I wish they would get on with fixing this. And also, since the criteria for +4 and +5 GOE is supposed to be perfect execution, I also feel that a flag needs to go up when the levels aren't there for the steps & pattern the same way judges' GOE goes down once they have been made aware that a UR has been called . . . or a fall on your choreo slide. Overall, I'm just annoyed with how out of balance the scoring is. (Yes, this change would make scores drop, and I realize that doesn't play well in sports but neither do competitions won with splats--and I'm not complaining about the judging at 4CCs just saying that an unbalanced system sets us up for debacles).
and it really bums me out that a team with the talent of h/d can get dumped so badly over program choice.
I think Hubbell & Donohue's demise is much exaggerated. They blew their cushion last season, when the combination of poor program selection, poor levels, Zach's inability to perform a rocker, and end-of-season pressure-related execution mistakes cost them. This year, they started on more even ground with the top players, started out late, and lost their clear #1 ranking at home.
C'est la vie. It's tough to lead.
But they are super strong skaters. They can cover the ice better than any team out there other than P&C. And that is apparent when they get on the ice. The complaining opposition-related yammering about body type and how they are too heavy/horselike/blah-blah-blah is codswallup and all arrows point to the likelihood that H/D can eat said complainants' favorites for breakfast if they get their ___ together. I honestly think they could have done it at U.S. Nationals. But Zach went all yardsale in the RD there, which is where they needed to establish a lead; and, like I said, it's tough to lead.
In conclusion:
We are heading into a Worlds with Nikita and Chock & Bates expected to contend and with Zach and Gilles & Poirier among those hoping to play spoiler. Now we look at that list . . . and I feel the odds of something not going according to plan are not slim. To give them all credit, though, they've all gotten here via a lot of work and perseverance, last year's Worlds went pretty well, and probably they will not all muck up in the same event.