Couple of similar threads, surfaced during my search....

Why couldn't it have been just a heart attack?

The death of Peter Clemenza...

Wasn't no heart-attack

“that Fat Clemenza” was a “walking heart attack” indeed Clemenza was puffing and panting climbing the stairs to kill Stracci

  • Why would Clemenza promise the Rosato brothers, Corleone rivals, three territories in the Bronx after he died?
  • If true, was Clemenza trying to pacify? the Rosatos because “The Rosato business was taking its toll on the old timer”
  • If true, wouldn't Clemenza need Michael's permission to carve up the Corleone territories and 'gift' them to the Rosatos?
  • If true, did the Rosatos hasten Clemenza's death by "their shenanigans" to get the promised territories sooner?
  • Did Roth make it up! stirring up trouble within Michael's New York operations and by backing the Rosatos?
  • Did Roth figure? Michael wouldn't want the Rosatos touched because Michael does not want his important business with Roth disturbed

Pentangeli: [Anthony's party] to Michael, disputing Clemenza's promise

“I weltched?”
“Clemenza promised them nothing. He hated those son of a bitches more than I do”

Michael “turned a blind eye” when Pentangeli 'disappeared' even though Pentangeli went to meet up, to "settle these troubles with the Rosato brothers" at Michael's request

Michael hanged Pentangeli out to dry nor took care of the 'dead' capo's family