How do I destroy object when monster can't find path

I have Monsters that are using pathfinding behavior. I want to destroy object when monsters can't find any path.

I know which object to destroy, but the thing is that pathfinding "failed to find path" condition runs forever, so even if monster find path it destroy the object.

Any idea for how to fix it or any other approach

Add another condition to the "failed to find path" event?

Maybe a boolean, set on a timer or a wait for signal?

LittleStain I did that and it didn't work, it is still running forever even if monsters find paths

NB in my code I spawn monster every second

check screenshot of the code

"https://drive.google.com/open?id=0B1pGW-xaP8VfM1hNZTFEeTgzd0U"