While there is little solid information about when Musa died, it is safe to say that he lived a life that many would be envious of. Not envious due to his wealth and power, but of his wisdom and good nature in how he used that wealth and power. $400 billion is an unfathomable amount of money for one individual to hold, but he did so with grace and humbleness by most accounts. At his time, he was so well respected that he was painted on the maps of the time.
While he lived in a world that had a fair share of war and strife, he was not a warmonger or tyrant that ravaged the world in which he lived. Some of the notions that we may not agree with, such as his slaves, were common at the time. While not all slaves in his world were treated equally, accounts depict a man that treated them with respect and made them as comfortable as could be expected.