When Michael said to Frankie, "I was glad you were able to keep the house after Clemenza . . ." (or words to that effect), it appears there was a chance the house could have gone to a "legitimate" owner.

As big as that house was, it would have been easy for Clemenza's wife and children to stay in the house with Frankie and his wife. As a matter of fact, who was the other woman standing next to Pentangeli's wife the day Frankie came home and found out Mike was waiting for him in the study? Clemenza's wife?