The Inhumans aren't exactly having the best of times right now in the Marvel Universe. This month marks the debut of the five-issue miniseries Death of the Inhumans, which sees Jack Kirby's cosmic characters being hunted for death by their former masters the Kree. The first issue wastes no time in gutting several tertiary characters, such as the Universal Inhumans back from Jonathan Hickman's Fantastic Four run, but so far the only real casualty of note is Triton, who was killed by a bomb. (The jury's out on whether Maximus and Lockjaw truly are done for.)
With four issues left of the book, there's still plenty of Inhumans for the book to kill off, and worth's examining just who may be left standing when everything is said and done. It's doubtful that Marvel would kill off all Inhumans. Some choices are very obvious--no one would be foolish enough to kill off the lovable Ms. Marvel, for example, Quake seems pretty safe thanks to Agents of SHIELD, and there's no way Marvel would let the adolescent Moon Girl be faced with literal death. At the very least, those three have a fairly strong security blanket, but other characters have fates that are much more questionable.
When it comes to the Royal Family, it seems currently safe to say that Medusa will live through the event. She may be recovering from a seemingly fatal injury, but she's cheated death before and thus far, this seems like a story that will affect Black Bolt most of all. Through his recently concluded series, we saw the Midnight King come to terms with himself and face some hard truths about who he used to be. With the Kree's new Super-Inhuman, a wicked figure named Vox who looks very much like Black Bolt and possesses his deadly vocal powers, it would be easy for the book to end in an all out brawl between the two, the King of the Inhumans giving his life so the remainder of his people can live on and he can die saving them after not really being there for them over the last few years. Medusa, though she's currently injured, could come back from it and proceed to rule the remaining Inhumans in the wake of her husband's death.
As far as Medusa's fellow Royals go, Karnak seems likely to survive the onslaught of the Kree. He literally found the flaw in death the last time he died, and his ability may be the one thing next to Black Bolt that actually stands a chance against Vox. Being dead has never stopped him, and he's more like their ninja. While the remaining Inhumans are fighting against Vox and his men, Karnak may decide to hit the Kree where they live and end the conflict that way rather than joining the others in an all out brawl.