First, note the differing green doors. The one on the wraithwing's side starts open, the one on the roach's side closed. That means you can kill the roach and escape, without anything being on the middle pressure plate, but only if the roach is the last thing you kill.
As for the wraithwing, if you think about the previous hint...
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×if you are in the middle chamber (you don't actually need to be on the pressure plate) and the goblin hits the pressure plate releasing the wraithwing, the wraithwing will move away from you. A lone wraithwing always tries to keep 5 squares away from Beethro.
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50th Skywatcher