It would obviously be a tragedy, and there are probably people attending the conference that are key to their specific research lab or small company that could seriously impact progress in their respective projects.
Overall, however, it wouldn't do that much besides make headlines. The fact is that research and technological development are so very rarely tied extremely closely to a single person. These projects are collaborative, and even with the head researcher being killed it is extraordinarily unlikely that you wouldn't be able to continue the research where it left off (hell, most scientists at research universities are old, and the fact that they don't grind to a halt due to deaths/retirement is proof enough). The biggest disruptions would be logistic, as sometimes the funding for these things can be very complex, and emotional (people not working due to grief, etc.).
And, to be perfectly honest, it isn't like every person at the TED Conference is some extremely innovative genius. I am not trying to downplay the achievements of some of the prominent attendees, but there's a lot of stuff that happens at TED that really isn't all that crucial or even interesting.
I mean, let's look at some recent speakers. Bono? I don't wish death upon him, of course, and I know he gives a lot of money/attention to charitable causes, but does anyone really think he is some crucial linch-pin in the world that would cause immeasurable harm if removed? What about Shane Koyczan, a rather mediocre poet who is only famous because his spoken word poem about bullying, a hot button issue these days, went viral on YouTube? Or Roy Finley, whose only apparent accomplishment is a community garden in Los Angeles? Am I going to miss Amanda Palmer, who just talks about how awesome Kickstarter is? Hell, I've seen a speaker (Puneet Sahani) at a TED Conference who literally just talked about how awesome it was to hitch-hike through India and hey, wouldn't it be awesome if everyone was friendly to one another?
So ... basically it would suck but not much would change. (Maybe I am biased, though, I have always felt the whole TED thing is massively overrated)
"Spare me your space age technobabble, Atilla the Hun." -Zap Brannagan
"It means they could've done some freaky human/demon hybrid thing." -Nightstalker, on Nazis