bah too easy..
see the line named common event?
link it to a common event (which you can set in common events tab)
and the common event will go:
change monster hp button (3rd tab of event command)
set it to 9999 and choose reduce hp, mark reduce hp can kill
so now we got rid of all the monsters.
now, set the "scope" to user of the item
get hp recovery to -100% (yes minus 100%= he is dead).
and .. that's it.
the user is dead, the monsters are dead and you lost the suiciding potion