I certainly suspect that he was seen off because at first he was not thought to be in particular danger. The withholding of medication s a possibility. And also his death mask did not seem to show the hallmark swelling septis deaths apparently often display. I do think Himmler saw an opportunity to rid himself of Heydrich, who he probably felt had far too much power and who was getting closer and closer to the Fuhrer. Himmler never replaced him. He took over many of his duties himself and put people like Muller, Kaltenbrunner and various other personnel in charge of specific departments and briefs. But he never actually replaced Heydrich, which is telling. There is no real evidence that Himmler helped to off Heydrich and certainly a number of Axis forum historians do not go for the idea at all. But I do. And I cannot shake the suspicion off either.