This happened both when I was playing the Library of Last Resort, and when I ran it with another group:
Lashonna and the PCs scry on Heskin, and realize that they've got competition in finding the Island of Last Resort. The group decides that they must act immediately, and they teleport straight from Lashonna's house to the Island of Tilagos. They are now hours ahead of Darl and his crew, so they effectively skip the encounter with the orcish pirate crew, as well as Krekie ambushing them in the maze of menhirs (since she hasn't even gotten to the island yet).
I realize that Darl's party will eventually catch up with the PCs in the island demiplane, but has anyone else encountered this situation? If so, how have you dealt with it? Just have Krekie join Darl's party when they attack the PCs on the Island of Last Resort?