That is a great question, Lana.

It's hard to get a read on Tom's feelings for Fredo, in general. I don't recall them interacting much in the movies.

Tom would know that Fredo is unable to handle running the Family. It's possible he would stay on to help if he didn't know that Fredo was involved in Michael's killing. But it's hard to believe that he would support an unqualified (and surely doomed) Fredo if he blamed Fredo for killing Michael.

In fact, thinking a bit more about this, Tom might well have taken the legitimate offers if Michael had been killed. He was not a muscle guy. Could he reasonably expect Neri and Rocco to be content working for him (or Fredo) for an extended period of time? Did he think that he (or Fredo) could withstand the pressures the Rosatos were putting on the Family in NY?

Tom was always loyal but also a very clear thinker. Without Michael, he might have gotten out while he still could.