Again I don't know what event you mean. If you want to stop something from happening when health drops to 0 then make an event to change a different global variable from 0 to 1 if health drops to 0. Then the events you don't want to run if this happens you can add the condition that the variable is 0 because when it changes to 1 it'll never run. So that locks out those event for the rest of the game if that's what you want.
Let me rephrase this because yeah it's a bit confusing.
Take this event:
cdn.discordapp.com/attachments/852976600068784148/1092831850671648778/screnshot-2.png
We'll call this the BossfightSequence.
I want that to run every time the level changes to a certain number. Only once though. Running that once, every time the level changes.
HOWEVER, when the health reaches 0, in this condition (https://cdn.discordapp.com/attachments/852976600068784148/1092831850919104542/actualscrenshot-1.png), I want the previous one (BossfightSequence) to completely halt, and pretend that it never existed, meaning only the new events in the health reach 0 event fire.