Daryll is dead. The walking dead kills off original characters every season, and Daryl is one of the last ones left. He also looks dead, so he probably is dead. He is not too popular to be killed. He probably is dead based on the trailer and the actor will do other things.
The cliffhanger is a pretty effective tool when it comes to TV and ratings. This sneak peek seems to hint that Daryl could be dead- since Dwight is seen on his (Daryl's) bike, wearing his gear. But it could also mean Dwight stole Daryl's stuff, or Daryl is hurt somewhere.
Dwight, without a doubt, shot the guy. On the other hand, precisely how promptly might Daryl's destiny be addressed in the new season? Is Daryl deceased? I are not able to answer that with 100% accuracy. All I know is that I think that he is dead, from what we have seen.
It is very rare for a protagonist of a TV show- even one like The Walking Dead- to be killed off. The sneak peek video is most likely nothing but a publicity stunt done to drum up interest for the show. Never fear, Daryl fans- he's probably going to be fine.