HI,
The audio clip is connected to the video clip above it with a little coupling. When you move the video clip by dragging it elsewhere in the timeline the audio clip will move with it. However, if you move the video clip by cutting and then pasting it elsewhere in the timeline, the video will get deleted. So, move your video clips by dragging and that should solve your deletion issue.
Another way is to slide the audio clip up or down the timeline so that the coupling is moved off the clip that you want to move, onto another clip. Then when you move the video clip by any means the audio clip will not be deleted.
Still another way, is to put your cursor on the audio clip and, while pressing down, pull the audio clip straight down to a lower audio well, until you see the coupling being pulled off of the video clip. Now the video clip and audio clip will be independent of each other so that deleting or moving the video clip will not delete the audio clip.
-- Rich