I'm so sorry.
I Agree with you. This is not right if the vet saw what looked like food in the stomach and did not think more of it after being notified that pup had not eaten in several days. A barium study should have been done. Any vet with an xray machine and baium can do this.
When something is sitting in the intestines, they can start to die off. The longer it sits, the more problematic things become. So yes, waiting several days may have caused his death. Abdominal palpTion should be part of any exam done on a dog with GI uoset.
You can file a complaint with our stTe veterinay board.