My debatable! theories, on further review....

Roth was slipping! I think too many variables in Tahoe shooting
I believe, the Tahoe shooting was complicated and risky even if it had been successful whereas Havana, Roth's kinda town, sure winner!

If Michael had died in the Tahoe shooting -
  • It doesn't seem to me, Pentangeli's neck is automatically on the chopping block
  • Roth couldn't have known for certain how Michael and Pentangeli's meeting would progress
  • In fact, Pentangeli could have persuaded Michael to back Michael's own man, in an obscure beef, a Street thing
  • There is always the chance that Tom, Neri, Rocco work out Pentangeli did not have the brains and could not have engineered the shooting
  • Tom and others may not factor Roth into the equation straight away but they all could work together and I believe Tom can restore order and save the Corleone business especially without Michael on his back!
  • Pentangeli joins in providing whatever muscle and help as required
  • Roth interesting himself in an obscure beef against Michael's man and in effect against Michael could have cast suspicions on Roth

If Roth had waited until Havana to murder Michael
  • Roth would have gotten Michael's $2 million
  • Roth would have used Michael's own money or part thereof to pay for Michael's own murder
  • Such a terribly unfortunate death, caught up in the midst of the rebel uprising in spite of being escorted in a military car
  • Nobody suspects any foul play because Roth loved Michael like his son and Michael was Roth's heir apparent
  • Roth carries on living like a retired investor on a pension with no Michael burrowing into Roth's empire