Quote: "by using the 'Destroy' action in the script for the triggerzone (after the audio has been triggered) the trigger zone can be used no more."
Correct, the "destroy" action will terminate the script.
Quote: " I think you might have to use a 'timer' (etimer) before you use the 'Destroy' action just to allow the audio to begin playing before the Trigger zone is shut down."
It depends on how it is scripted, etc. It IS better to use an etimer as you suggested, give it a 1 second time, then destroy the script. Even when the script is destroyed, the sound will play to the end then stop.
There's no problem that can't be solved without applying a little scripting.