Short answer: It gets pushed out in other places. Long answer: When you try to do destructive interference, you do it only in specific places, you have valleys

Short answer: It gets pushed out in other places. Long answer: When you try to do destructive interference, you do it only in specific places, you have valleys and peaks somewhere else. Energy from valleys (detructive interference) just enlarges peaks and makes them brighter. As first commenter on that topic said, you can't make destructive interference without making constructive one in different place, so energy is not lost.