Thanks to some chatter from the showrunners, trailers, and upgraded contracts, we know a few people who will definitely be making it off the island alive: Slade Wilson, Laurel Lance, Dinah Drake, and Rene Ramirez. David Ramsey, meanwhile, has also confirmed Diggle makes it out alive, which isn't much of a surprise since he's a member of the original Team Arrow.
As for who's left, even though Felicity divides fan opinion it's unthinkable that the writers would kill her off at this point - and certainly not in that fashion - and presumably Thea survives too: there's still plenty she needs to do, and there's little point having Malcolm sacrifice his life for hers if she's going to die moments later anyway. Curtis and Felicity were both mentioned in the Season 4 premiere of The Flash too, suggesting they survived (unless the timelines really don't match up).
Both Talia and Nyssa al Ghul were on the island too, and there's a good chance that one will survive and the other dies, to give some more interesting development for future storylines.