I was really disappointed that they Kelled Michael off with his heart problem conveniently (for Phelan) to stop him being murdered.
Phelan was going to murder him, it would have made a much better storyline to have him bludgeon him then try to get rid of the body and cover his tracks, than "Oh, he died of a heart condition, wonder why he was on the builders yard?"

Was anyone else disappointed about this missed opportunity for a "gripping" storyline?

In a way Phelan DID kill him, by omitting to help him, by resuscitation and not calling an ambulance
Killing by omission

Yeah but it will just be seen as a tragic "accident".

No, because a villainous character murdering someone in cold blood has been done to death. We have just had one with Kylie. And knowing Corrie someone would be wrongfully arrested for Michael's disappearance/death, whilst Phelan skulks around getting off with it.

The heart attack was so much better and quite haunting due to Phelan allowing Michael to die rather than get help.

In common law, we all have a 'Duty of Care' to assist and call for help for somebody ill or in danger. If it could be proved that Phelan knew Michael was dying of a heart attack, he could be prosecuted. I think that Michael was killed off too so, as there was a lot more potential in the storyline. Will Phelan now have to be written out?

I think there are too many tragic deaths in Corrie.