Yes, there’s a ton of tragedy in his life—all self-inflicted. He had free choice at every turn, and he freely chose the Mob life, with disastrous results. Here are four major examples that I’d like your opinions on:

First: He was right to think Sollozzo would try to kill his father after the failed hospital attempt. He was wrong to believe that only he could save his father, by killing Sollozzo and McCluskey. Ironically, an idea that Michael himself had suggested could have been modified to solve the problem bloodlessly. The Corleones could have fed the newspapermen on their payroll the story about McCluskey being a dishonest cop mixed up in drugs and murder before, not after, the trigger was pulled. McCluskey was on the take all his life, and the Corleones had all the details because they paid him. The newspapers would have given that story such headlines that the Police Commissioner would have been shamed into providing Vito with an army to protect him, to save further embarrassment. McCluskey and Sollozzo would have been neutralized without any bloodshed. At minimum, McCluskey would have been transferred or suspended pending investigation; with pressure from the Corleone judges, he’d have been indicted for taking bribes. Sollozzo would have been arrested and probably deported as an undesirable alien. With McCluskey alive, the cops would have had no reason to crack down on all Mob activities. There would have been no Five Families War of 1946, leaving it a contest between the Corleones and the Tattaglias—and as we know, Tattaglia was a pimp, alone he could never have outfought Santino. Michael could have married Kay and gone back to college (and we would have had no Godfather Trilogy!).
Instead, Michael chose to kill Sollozzo and McCluskey, setting in motion his abandonment of Kay, his Sicilian exile, the Five Families War, Carlo’s betrayal, Sonny’s murder, Apollonia’s murder.

Second: He could have resumed the legitimate life after returning from Sicily. He could have said to Vito: “Pop, I was wrong to distance myself from you. But I atoned: I saved your life. And I paid a heavy price: two murders, abandoned my beloved fiancée, lost months out of my life in Sicily, lost my beloved bride to a bomb intended for me. We’re quits. Now you run the family…Oh, not feeling well enough to take the reins? Fredo not equal to the task? Sorry, Pop, that’s not my problem. Besides, you always said you didn’t want this for me—you wanted me to be a pezzanovante. Well, I can’t be Senator Corleone or Governor Corleone if I’m Don Corleone. Bye-bye.”
Instead, Michael chooses to become the Don, setting in motion Tessio’s betrayal, the Great Massacre of 1955, Connie’s widowhood and breakdown, and the beginning of Kay’s disillusionment with him.

Third: After moving to Tahoe, Michael could have retired behind the walls of his compound and invested his wealth legitimately—even putting money up-front in the legal casinos of Nevada.
Instead, he chose to hide his ownership or controlling interest in three hotels; muscle Klingman out of his interest in a fourth hotel; dominate the New York mob scene through Frankie Pentangeli; undercut Pentangeli through his support of the Rosato Brothers and their drug-dealing; stake Fredo to ownership of a brothel, and plan for a huge international expansion of his gambling empire through his deal with Roth. Results: Fredo’s betrayal; the machinegun attack that nearly killed Kay in her bed and scared the bejesus out of his kids; Kay’s estrangement, abortion and divorce; Anthony’s estrangement; Fredo’s murder (and a host of other killings).

Fourth: he was “legitimate” in GFIII—but was he? He whines, “Just when I thought I was out, they pull me back in.” But he was never out. He either was still a member of the Commission or influential enough to keep Zasa from rising (so Vincent tells us). He laundered his Mob cronies’ money through his “legitimate” businesses (maybe through his foundations) and cut Zasa out of his share. Result: the machinegun attack in Atlantic City that killed all his pals and precipitated his diabetic stroke. It wasn’t enough that he became a Papal Knight: he had to dominate International Immobiliare by bribing crooked-as-a-corkscrew Archbishop Gilday, setting in motion Altobello’s betrayal and putting him against Don Lucchese, who was far more powerful in Europe. And, in an act of supreme irresponsibility and egotism: told that Sicily’s top assassin—“a man who never fails”—has targeted him, Michael gathers his entire family around him in Sicily, making them all sitting ducks. Surprise, surprise: his beloved Mary gets killed and his budding reconciliation with Kay is nipped in the bud, leading to his own, lonely death, attended by a little dog.

Michael succeeded--in turning everything he touched into death, including his own.

What we do know is Mike was alone. After Mary's death he probably shut down completely. It looks like he even went blind.

Blindness, through retinal damage, can be a consequence of diabetes. But it is easily avoided through medical attention and is almost unheard of in countries where doctors are available.

If Michael is blind, that's a clue that he may have shut down to the point that he stopped treating his diabetes. Untreated diabetes also leads to cardiovascular disease, which was probably a major factor in his death.

Perhaps the end of Michael was self-inflicted, over a period of years.