I really hope for her children's sake she is okay. I am sure law enforcement has done this, but I wonder if they are also searching manifests using her prior name (Ana Knipp--listed on the fed affidavit linked a few pages back-- think she was married before?) or her maiden name, which is something else (since it's not public yet I won't post it, but it starts with L and is definitely a Serbian/Croatian name, found on radaris).
Also, if she did leave voluntarily, she seems intelligent enough to get another phone/CC's. I really can't tell if this is going to be a Gone Girl situation or a Murdaugh one. In the alternative both Ana and Brian could be in on it-- she disappears, probably with some funds the feds dont know about yet, and then he can try to get out of jailtime to take care of the kids.
ETA it doesn't seem weird to me to have a NYE party before traveling early-- my friends with young kids tend to celebrate "fake midnight" early so they can get the kids to bed at a normal time, and then they themselves pass out at 10 PM lol.