Joss Whedon was not even present for the Avengers: Age of Ultron panel at Comic-Con, but according to reports, the footage shown ended with a an image that might prove predictable to many a Whedonite: Iron Man coming across the rest of the Avengers, dead, sprawled on some cosmic staircase. Could Joss Whedon be killing the whole team!?!??!?!
Well, no, of course not (Marvel's got sequels to make), and obviously this arresting image plays into some sort of terrible fantasy Iron Man is witnessing and nothing else. But I'd take the argument one step further: we shouldn't fear Joss Whedon killing off anyone important, because that's not his style. Going back through his TV career all the way up to The Avengers, one finds he always goes for the cheap, but effective kill—the cuddly character who everybody loves but isn't really crucial to the plot—to raise the stakes.
In season two of Buffy, when evil-Angel has to kill someone to make it clear that he means business, he offs Giles' nice librarian girlfriend/keeper of the gypsy curse Jenny Calendar, a genuinely brutal and horrifying moment, but directed at a recurring character who served no vital function in the plot. Tara's death in season six (she gets added to the credited cast only for her final appearance) was equally horrifying but again almost feels like Whedon is picking on his most defenseless characters. Yes, each time the stakes were raised, but it felt a little cheap and easy.
In Angel, it's Fred who bites the dust, which is a pretty major move, but she just turns into the demon Illyria and continues to have a part on the show (it's hard to know what direction Amy Acker's performance would have headed from there, since Angel was canceled at the end of that season). He didn't have enough time to needlessly slaughter anyone in Firefly, but he picked things up in its spinoff film Serenity, offing Shepherd Book and, most notably, Wash (Alan Tudyk), again citing a need to "raise the stakes."
The problem is that the stakes don't truly feel raised when he pulls off these twists—instead, it feels like the big shocking death has happened and everyone else will be just fine. Wash's death, which is intentionally out-of-nowhere and random in nature, provides a sudden jolt but has no real lasting power. We don't get any more Wash in any Firefly properties just because that final battle in Serenity has to feel dangerous? Or Anya in Buffy? He even pulled the same stabbed-through-the-heart trick with Agent Coulson in The Avengers, again to raise the stakes and push the plot forward, but of course that was undone to give Agents of S.H.I.E.L.D. a recognizable lead character.
There are times when Whedon has gotten it absolutely right. The death of Buffy's mom Joyce, and the episode "The Body," remains a devastating exploration of the hollowness and randomness of death. But it works almost by subverting all the tricks Whedon usually pulls in his plotting.
I write this as a longtime Whedon obsessive and fan who thinks he did a great job on The Avengers (and is nonetheless still clearly steamed about losing Wash in Serenity). Every great writer has a bag of tricks they rely on, and Whedon's bag of tricks have provided me so much pleasure over the years. I'm just begging him—if you're gonna kill someone off in Avengers: Age of Ultron (and rumor has it he might), really try to make it count. If it's just another plot twist to raise the stakes, I don't think I could take it.