I think it's highly unrealistic to think Michael would feel sad if he were alive to hear of Tom Sneddon's death. Michael's mother Katherine said in David Guest's documentary she hates Sneddon, and I presume Michael opinion would be the same.
I have no idea how Michael would react in private if he heard about Sneddon's death, but I doubt he would feel any sadness because Sneddon went out of his way to destroy every single part of Michael's good name and life, consequences of which Michael's child, parents, brothers, sisters, nieces and nephews will have to live with forever. I just think the news of hearing of Sneddon's death would have been good news to Michael (I doubt he would have been jumping around laughing) and a huge relief that would have taken a lot of pressure off his life as Sneddon had a vendetta against Michael.
The gun shot at the end of the song D.S in my opinion gives a good idea of what Michael would have thought.
Tom Sneddon was a criminal, and he's death makes this world a better place. I have no sympathy for his family, because I doubt Sneddon had any sympathy for Michael's children and parents when Michael died, because Sneddon is a huge reason why Michael is dead.