Actually Turnbull even if Tom had known and I agree Tom should have that “Pentangeli had survived and was in Federal custody, to be used as a witness against Michael”

• What would Michael have done differently? though Nothing!

Michael in reality could never have taken the fifth amendment to the US Constitution

So Michael would still have lied under oath, denied all the charges and committed perjury
ie: It's up to five counts of perjury rap remains unchanged

Michael wanted to show that he has nothing to hide, nothing that would incriminate him
So Michael taking the fifth was never an option

Whilst knowing about Questadt confirmed it was kangaroo court [no surprise! there] it was not pivotal in acing “what the hell happened here”!