According to Larry Geller, Elvis' so called spiritual mentor, Elvis realized that he had a problem with substance abuse. After he finished the tour he was on (at the time of his death), he was going to take a year off and live in Hawaii. He had already found a house there. He was going to get off the drugs and get in shape. He wanted more than anything to be a serious actor. Also, he was going to get rid of more of the Memphis Mafia and Tom Parker. So, if things had gone according to Elvis' plans, he would be an actor. I would like to think that he would still be singing, but not in the movies. He loved gospel music, so something in that direction could have happened.
Personally, he might have grown up enough to get married. Who knows, he might have had other children. Now wouldn't that be grand.
We already know that he would be a grandfather. I would like to think that he was enjoying his life and his grandchildren.