If possible, I'd like to get a simple factual confirmation about which Jarvan it is that Sion just killed. There's some time-sensitive Factions lore that needs doing, and "which Jarvan" does bear on the story. Xin Zhao's role as bodyguard is currently more central still. I'll probably just write it fast and then do a retcon as necessary, but i'd like to at least write it with the most likely outcome in mind, to reduce the amount of rewriting that's necessary.
I'd hope that it's Jarvan I. Sion's body could have been preserved somehow (maybe in that giant mausoleum) until Swain and company raised him up. The problem with it being Jarvan II is the potential clash with Xin Zhao's lore. I suppose Xin's lore could be updated to have him being saved by Jarvan III when he was younger, though Xin being oddly long-lived, and having seen multiple generations of Jarvans, was a nice touch IMO.
I'd also hope that Xin Zhao would keep his role as royal bodyguard, but I have kind of a bad feeling that they'll rework it to him just busting out of the arena himself (there's a tendency to make characters very self-reliant, and I can imagine them bristling at the idea of him being rescued, though I think it adds a good dimension to the story) and then going off to have some kind of magical adventure that has nothing to do with Demacia.
**Current assumption:** Here's what I'm currently going with while I write the epilogue to Hextech Revolution — Jarvan II rescued Xin Zhao from the arena. Sion killed Jarvan II. Xin Zhao pledged to protect Jarvan III out of contrition for his failure.
Either way, though, I'd welcome either Rioter Word of God or some reasoned predictions about what's actually going to happen.
**EDIT:** Summoner Entropy of the Riotous Fists Clan has confirmed that it was Jarvan I after all!