My take, for what it is worth!

Roth was undoubtedly a danger to Michael from day one and had to die.

It has to be the Cuban Military who arranged to get Roth out of Havana alive after saving Roth from being murdered by Michael's bodyguard in the hospital room

I believe, the incredibly resourceful Roth would have already had in place
Plan A – Tahoe bedroom shooting
Plan B – Michael's murder in Havana
Plan C – Senate hearing / brilliant perjury trap

Fair enough “Suppose Michael hadn't ordered that Roth be killed at the airport. He might not have had another shot at him” and Michael certainly wanted Roth killed publicly at the airport

What did Roth really know about Michael? the recipient of the Navy Cross, who has never been arrested or indicted for any crime whatsoever No proof linking Michael to any criminal conspiracy

Roth probably knew plenty about Vito and the Corleone family but nothing concrete that would “pull Michael off of his "legitimate" pedestal, and send him to prison”

Roth can tell about Roth and Michael's 'legal' gambling partnership! but precious nothing for the supposedly "priceless resource" to rat Michael out

I believe, the clever Roth would know this and would not incriminate himself knowing Roth cannot 'touch' Michael, the exact reason Roth won't sing There is No deal!
Roth would have continued playing the part and maintained he is a retired investor on a pension

I doubt anyone - FBI, Questadt - would be game enough to take on Michael Corleone again after the dismal failure of the senate hearing especially on the desperate 'ramblings' of an old man in custody trying to pitch an "attractive proposition" to rat Michael out "in return for lifetime protection and lenient treatment"

Whilst “No one was indispensable” Michael would not sacrifice any of his men [especially his top men like Neri or Rocco] whom Michael selects and counts on them to carry out their jobs successfully and get away with it

Every member is pivotal link in the chain
If lost as unavoidable collateral casualty, so be it but not intentionally "expendable" nor would Michael want to lose / sacrifice his men

Michael does not come across to me as someone who would cut off his nose to spite his face