Many characters have died on the Arrowverse, some of them only temporarily, some multiple times, and few of them have even died permanently.
In the case of Lance sister’s Sara has died/supposedly died multiple times, and her sister Laurel died in the hands of Damian Darkh in season 4.
Sara has now departed Arrow and is one of the major characters in Legends of Tomorrow. Where as Laurel’s death being permanent, at least for now.
Katie Cassidy has since Laurel’s death returned in 100th episode of Arrow, and numerous appereances as her Earth-2 doppelganger Black Siren in The Flash and Arrow.
The producers of Arrow have repeadetly hinted that there is still more to come from Laurel Lance/Black Canary. And during a recent Q&A event EP Mark Cuggenheim hinted at how Laurel may reappear in the Arrowverse.
“We have an idea for how to see her again, but we haven’t made a deal with her yet. She’s not a series regular anymore, so we have to make a contract with her and she’s got to be available, and we haven’t had those conversations [yet]. But we do have an idea. We know exactly what we do want to do.“
There are literally innumerable possibilities on how Laurel could return, with many resurrection possibilities, Legends of Tomorrow’s time travelling and Flash’s free run with the multiverse. But many fans would probably be satisfied with even a brief apparence in a flashback.