Sounds like Shin Megami Tensei. Which I love. <3
This is what you probably want to do then.
Have your event as a regular Action Key or whatever where you can negotiate with the demon.
Once the demon gets pissed, that's when he turns hostile, right? Let's now make him into an enemy...
Use this Call Script: (This is located in 4.3.6. in the manual)
$game_map.rename_event(EVENT_ID, 'NEW_NAME')
Change the name to include the enemy tag on there. Now turn on a self-switch to a new page, and have that new page only function if that self switch is ON. Once you kill the enemy, blah blah, put all the event stuff you want in there.
Now, if you want that enemy to possibly come back or something when you return to the map, then in the event when he's killed, just turn off the self switch, rename the event back to the original thing, and erase the event.
...I haven't really evented or even used Blizz-ABS in ages, so maybe there's a better to do this... But it sounds like this would work. >_<