Nope, they're out of Ravenloft for good, but one of them keeps asking about Lenk. Who was 7 years old when they left so they have a good 20 years before he becomes a threat, but since their time in Ravenloft was 2-3 weeks and they were away from the Prime Material for 2-3 days, they assume (correctly) time can be relative.
After all, I've already used a chronomancer that hopped back from the future to tell them stuff.
Yet, I plan to use other things from their previous adventures. When fighting the KToa, in an adapted Shrine of the KToa, they escaped leaving around a marilith (summoned by the KToa goddess herself). I described the Marilith being out of control in a big final battle but there was little a party of 10th lvl chars could do against a Marilith
and about 200 KToa that were hunting them.
I'm sure they've already forgot about the Marilith, thinking that as the shrine was destroyed (long story), the marilith would be banished back I guess. Well, they're wrong. The Marilith is still around. They've insulted her (by not escaping from her twice) so after a couple of years of doing fiend-stuff she'll look for them.
But I will use Lenk in future campaigns in Ravenloft
After all, the PCs never took Ladislas' spellbook... it lies there in the coffin the sicko used to sleep and as a desk. (I think that's a between-the-lines reference to his sexual preferences)
The Talons hastily looked for enemies there, found only the destroyed guards and moved on.
So a lot of Ladislas' work is there, along with the book Myrcea kept with the notes and entries. One of the first things adult Lenk will find, the only thing to connect him with Myrcea will be the book with the PCs names.