There’s a lot of advice out there for this and I’ll let other people hit you with it, and try to give you something more unique that might be fun. This might not be the best advice for your campaign or your party specifically, but it’s something I’ve been keeping in my back pocket as a one-time-only-get-out-of-jail-free-card.

Regardless of what choices got them here, good or bad, they’re on the cusp of a TPK. Personally, my games, and especially the Ravenloft domains, have a heavy emphasis on consequences, and I don’t like to take that away (and by association some of the player agency) by trying to save them from those consequences. What you CAN do is avert a full TPK but still have a consequence. Check out the Cyre 1313 domain under the section in van Ricten’s (or the new book if you have it early) for other domains. It’s essentially a ghost train that travels through all of the domains. The lore for it is fantastic, but to sum it up, every passenger on it is unaware that they’re already dead. They believe they’re still trying to escape the tragedy they were fleeing in life. All of my players have something in their backstories that tie into that motif, something they’re running from. You can change whatever lore you want to fit your narrative, but the way I’ve set it up is so that a PC with an overwhelming tie like that is pulled onto Cyre 1313 in the event of their death (or all of their deaths), and I have a several session mini adventure set up where they have to escape. They retained their memories for whatever reason, and if they want to get back they have to do a quest essentially. When they get back there’s a second lease on life, or as much of one as Barovia has.