Personally I think you did the right thing trying to give him every chance. Had he pulled through - and it sounds like he very nearly did - you'd be feeling very differently about your decisions. It's just bad luck he didn't and after all it's all the same to him. Don't beat yourself up about it :)
There's an airstrip and some model plane flying club near the yard... I very much doubt the horses would care about a drone. One rider did nearly get killed by a plane though. They were on the airstrip at the time. It's grassy and looks perfect for a canter.
Oh goodness I saw this earlier today and couldn't help but laugh even though it's not really a funny situation to be in if you're not a particularly confident rider. People were pointing out he might perhaps have a dog at home called Fenton:https://www.youtube.com/watch?v=3GRSbr0EYYU