Not necessarily. It could have been either of them who was scheduled to do the early WBR. Alice was on-air until 12 midnight last night with editions of World News Today. It's my guess that Caroline was scheduled, but was running late, or Victoria Fritz may have been on the rota, but was unable to attend.
Aaron Heslehurst is filming in the Netherlands, so it wasn't him who didn't turn up
David Eades did the 8am slot on World today, and is now doing Impact. I don't recall seeing David on Impact before. Karin Giannone was the presenter of GMT. And, as already stated above, Laura Westbrook was in for "The World Today" at 5am.
She covers on Impact a few times (mostly during Mishal's exit) & also occasionally presented the TWT 5am-8am during the period when Naga moved to Breakfast
I have a suspicion we won't be seeing Kate Silverton back on our screens anytime soon. She returned from Maternaty Leave a couple of months ago but has only been on radio. There isn't exactly a shortage of national presenters, especially with the increasing prominence of Clive Myrie and Simon McCoy on News at One. Also when George Alagiah's returns in the (hopefully) not too distant future, there will be even less need for her.