My take, for what it is worth!
“Michael was
frantic to get Fredo on that plane out of Cuba†because Fredo was still Michael's brother and wanted Fredo safely out of Havana “looking out for his brother's welfareâ€
“At that particular moment†Fredo's safety and welfare was the urgency not “pumping him for informationâ€
Besides Michael didn't know
then how deep Fredo's involvement with Roth was....
Michael was just relieved that Fredo was safe
So “Michael merely tells Tom to get word to Fredo that he understands that Roth misled him†to assure Fredo everything is all right
Fredo was back at Tahoe like no big deal!
When Michael “learned that Pentangeli was alive†Michael went to pump Fredo for information if any
Only then Fredo's true treacherous betrayal came to light at his boathouse outburst and sealed his fate Fredo's situation became untenable
Did they have to die? I too believe Fredo was going to be spared "but that violent, resentful outburst in the boathouse--Fredo never making an apology, and admitting that he betrayed Michael for personal gain--sealed his fate" Fredo's situation became untenable
"Michael was frantic to get Fredo on that plane with him out of Havana" For Fredo's safe passage out
Michael's "get word" to Fredo was to assure Fredo everything is all right
