Originally posted by Mignon:
Even if it took years for Mama C. to pass away what would Michael have done with Freddie in the meantime to ensure he wouldn't go against the family again? 
With Fredo staying in the Tahoe estate most of the time, having lost all his rights in the family business and being in a mentally unstable state (as his "Hail Mary" lines near the end suggest) and with Roth and Ola dead, Michael had few things to worry about. Presumably, he would also have him watched every time he went out of the estate.
