Early reports of Laurel Lance's demise have been greatly exaggerated. During the Arrow SDCC panel, it was announced that Cassidy was given a similar deal as Wenthworth Miller's Captain Cold and John Barrowman's Dark Archer where each respective character will be a regular across each of the 4 DCTV shows currently airing on The CW. In Cassidy's case it's currently unclear whether she'll appear as Black Canary or her Earth-2 doppelganger, Black Siren (or perhaps even both). We should have clarification on her role soon but in the meantime, revel in the news that this isn't the last time you'll see Cassidy on The CW and there's still a slight chance Stephen Amell's Oliver Queen will follow comic book canon and enter a romantic relationship with Canary over Felicity Smoak.
We'll keep you posted as the story develops.