This article contains spoilers for Excalibur #10.
A rogue member of the X-Men just killed Betsy Braddock, aka Captain Britain. Jonathan Hickman's X-Men relaunch has seen the entire mutant community gather on the living island of Krakoa, establishing a new mutant nation. It's caused political chaos worldwide, and tension is ramping up to the extent Marvel's World War III feels almost inevitable. Even other planes of existence have been affected, according to the mystical principle of "as above, so below."
Matters haven't been helped by Apocalypse, who proudly considers himself the First Mutant and has an agenda all his own. Tini Howard and Marcus To's Excalibur has seen Apocalypse effectively conquer Otherworld in the name of the X-Men. He's placed Jamie Braddock on the throne of Otherworld, an Omega level mutant with the power to tug on the quantum strings binding the Multiverse together. Like many reality-manipulators, Braddock's powers appear to have warped his mind. As a result, he is dangerously unstable.
The consequences of Apocalypse's actions are becoming clear in this week's Excalibur #10. His experiments in Otherworld have already fractured reality itself, and he uses his sister Betsy Braddock's mind to build a new one. Unfortunately, Betsy is particularly conflicted right now; as a mutant she is Krakoan, but she has also become the new Captain Britain. These two aspects of her identity are at war within her, as she struggles to figure out how to operate in this new status quo. Consequently, when Jamie rebuilt reality around Betsy's psyche, it was a world at war. The UK and Krakoa are trading fire, with Excalibur caught in the middle of it. Naturally, the siblings come to blows - and Jamie, being lord of reality itself, lashes out. The result is apparently fatal for poor Betsy. Captain Britain is killed, and reality fractures once again.
Excalibur #10 is an explosive rollercoaster of an issue, but of course, it's too soon to consider Betsy Braddock gone for good. For one thing, Betsy is a mutant, which means she can be resurrected using Krakoan technology. Death has always been something of a revolving door in the X-Men books, and that's never been more the case than in the Hickman era. Of course, there is no way of knowing whether or not a resurrected Betsy would retain the mystical connection to the Otherworld that makes her Captain Britain.
But the X-Men's Krakoan resurrection protocols may not even be necessary. Jamie Braddock is lord of reality itself, and in Excalibur #10 he reveals he has created at least one duplicate of his sister. She's otherwise engaged in Otherworld, battling against unknown threats. Jamie has both killed and resurrected Betsy many times in the past, and there's no reason he couldn't do it again. When Jamie is involved, reality is fluid, and anything could happen in next week's Excalibur #11.