Yes, the thing is, he was an older man and older men sometimes can't do the same things that they did when they were 20. Michael could still dance, but he had sleeping problems. People the knew him said that after doing a just one show on tour he couldn't sleep for days, now just imagine him doing 100 or more shows. That's why he used drugs. He told one of his friend, "If I didn't need to take drugs I wouldn't."
And another bad thing is that the drug he used was only supposed to be used in hospitals. And the doctor that gave Michael the drug didn't know how to give the drugs properly, he didn't even know how to do C.P.R. correctly!!!!. Michael's doctor was going to the bathroom and on the phone while Michael was dying!
Michael REALLY wanted to do the This is it tour, for his kids and his fans. So he would have done it if he had lived.