Originally Posted by Turnbull
Extract:
If so: I believe that Michael regarded Pentangli as expendable. When he dispatched him to "settle these problems with the Rosato brothers," he was asking Frankie to put his head in the lion's mouth. If Frankie survived and settled the problems, so much the better for Michael--one less issue to trouble him. If Frankie was killed, more affirmation of Roth's perfidy. But, by the time of that scene in Roth's hotel room, Michael had already determined that Roth was a dead man.
Pentangeli, Michael's muscle, was too valuable to Michael and I believe that Michael wouldn't “regard Pentangeli as expendable”
My take, Michael didn't need any “more affirmation of Roth's perfidy”

Michael and Pentangeli's conversation
Originally Posted by Lana
Extract: If Michael loses his muscle and becomes just another casino operator, easy pickings for anyone which would be bigger worry for Michael

If Michael perhaps expected the Lion maybe to maul! Pentangeli but not kill him
Quote
Michael: Who had Frank Pentangeli killed?
Roth: The -- Rosato brothers
Michael: I know -- but who gave the go ahead I know I didn't