Amadeus is a good play and the film adaptation was great. The trouble is, too many people watched it thinking that it was a history lesson rather than a work of fiction. That's the audience's fault, not the writer or filmmaker's.
In reality, Salieri and Mozart got along fairly well. The person who commissioned the Requiem Mass from Mozart did indeed try to steal the work and take credit for it after Mozart's death, but that man was Count von Walzeg, not Salieri.
Saleri went on to teach Beethoven and was saught out by Beethoven for many many years after Beethoven became famous.