TED is a meeting of several important figures in dozens if not hundreds of fields. So, due to terrorist actions, the TED conference is bombed and everyone attending is unfortunately killed. How does this affect the world?

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"I will not be pushed, filed, stamped, indexed, briefed, debriefed,or numbered. I am a free man. My life is my own" Number 6
The Prisoner

Here's a quick rundown on exactly who TED are, for those who don't know about them... which I sorta suspect is most people reading this.

With such a vague OP, it's difficult to say what would happen other than yeah, it's going to kind of suck for a lot of companies and scientific fields. Assuming that high-profile targets such as Bill Gates were involved however, then regardless of what the implications for the world of science are, it'd be seen as the most high-profile terrorist attack since 9/11, and would lead to some serious shit happening to whoever claimed responsibility, along with any countries housing them, not to mention the domestic socio-economic consequences and likely curtailing of civil liberties.

not much.

for the number of smart engineers and scientists in the world, losing a few hundred in the audience won't do much more then but hiring rates in San Francisco up for the next month.

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"Aid, trade, green technology and peace." - Hans Rosling.
"Market forces are a good servant but a poor master." - Zaune

What a stunning display if selfish callousness and ignorance.

Without knowing what these individuals are involved in and at what level, it's difficult to say; but if they drive complex and time critical probes it could easily cause serious disruption. The loss of project familiarity and organisational competency will hit smaller companies especially hard.

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)

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"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