I have barrier on my map which I want to be removed once the 'ai of choice' has died.

I think the script will start out like this:

(script dormant remove_fire
(sleep_until (<= (unit_get_health captain) 0.6))

But I just need someone to tell me what the script will be like if I want to remove a scenery from the map once 'captain' dies.

Sure. Here's an example:

(script dormant remove_fire
	(sleep_until (<= (unit_get_health captain) 0))
	(object_destroy <scenery object name>)
)

I don't know why you set it to be (<= 0.6), because that would mean that the script considers the "captain" biped dead when his health is at or below 0.6, not 0. So, I changed it to 0, since you say you want the actions to be performed when the biped is dead.

Also, if you're going to put a sleep_until in a dormant script, then you have to make sure that you're going to wake that script from another script before the captain dies.

Anyways, that's the command to get rid of the scenery. You just need to name the scenery and insert the name there.

Thank you, this helped me out a lot, I just need a little more help with giving my captain keys biped a weapon.