I saw someone point out on tumblr: the director for 11x20 tweeted the picture of JPJ in the car and said they were shooting the first scene of 11x20. So, if a character is dying in a car crash in 11x21, I don't think it would happen in the first scene of the episode before it....in both sides (20 and 21) there seem to be car accidents, so my guess is that Webber is driving and witnesses the accident in 11x20 and maybe stops to help or something?
Also since webber had a NDE experience in season 9 finale, if they were planning to send him off, i think they would just send him to boston with catherine...another disaster for webber seems repetitive, but that's just my opinion.
I dont think they would kill derek, even if patrick desperately wanted to leave. he signed on through season 12 and it seems like they gave him a lot of schedule flexibility. why would he want out after they've already been so gracious to him?
I would be more concerned about those whose contracts are up this season (do we know anything about owen, april, jackson, arizona contracts?) or the characters who haven't had any story line or focus (especially alex, but also jo and stephanie).
any the sides say the patient hasn't shown brain activity. does that actually mean the character is going to die?! they also change the sides a lot, so "no brain activity" could actually be "limited brain activity" and whoever it is could make a miraculous recover by the finale?