sadly having a fish jump out is the best way to become really careful with potential jumpers. my 8 inch silver arowana jumped out a long time ago and i've never had another jumper since.
I feel for you. You feel like you let them down when something like this happens. I left the house hose on in my 7000 gallon koi pond one night when the well pump wouldn't come on, just to top it off. I forgot all about it untill the next morning. I lost 30 koi. It still hurts to think about. I shut the pond down. The only thing that really helped was setting up the pond again and looking for some more koi. Which I have. We all break our cardinal rules at times and some end in disaster. Just try to make some kind of positive come from it. Again sorry for the loss.RIP