Let me clarify: I want to know how historians believe he died and where his tomb might be, if he has one
The most accepted theory based on his symptoms was that typhoid fever or malaria killed him Source. It is perhaps more intriguing to imagine that he was poisoned with strychnine, which is a possibility. His men had become tired of the campaign and they did not like how he started to adopt aspects of Persian and Egyptian culture, not to mention many of those close to him hoped they would inherit his empire.
It is said his body was taken to Egypt, from where he planned to rule his empire once he arrived there. However the tomb of Alexander was never found. If the assassination theories are true then it is entirely possible there is no tomb of Alexander, that they simply disposed of the body in an unmarked grave. Otherwise it is possible that this tomb was in the ancient city of Alexandria, which is now mostly sunk to the bottom of the Mediterranean, or perhaps it is somewhere in the desert still undiscovered.
re the location of his remains, you may be interested in some previous threads (tl;dr: somewhere under the modern-day city of Alexandria)