I've sent my horse out for training. I worried while he was gone.
But if he died while he was there -- which is always a possibility -- and if I concluded that he had probably died of natural causes -- why on earth would it be my "responsibility" to warn other horse owners about that trainer?
P.S. My horse is 13.3. I'm 5'6 and not slim. My horse doesn't feel remotely ponyish. A lot of quarter horses are small, stout, and strong.
Also -- of course we're all sorry your horse died.