Yaakov had just stolen the brachos. Esav found out what happened and reacted very harshly. he said he was going to find and kill Yaakov. Rivka decides to send Yaakov away for a while to keep him safe until Esav calms down. Yitzchak calls in Yaakov, blesses him, gives him some instructions about looking fo a wife, and then sends him on his way.
Why did Yitzchak not say a word to Yaakov about what he had just done? Not a word of criticism, not a word looking for an explanation, nothing. Yitzchak acted as if Yaakov had not just deceived him to steal the much desired brachos. Why?
Sometimes things happen that make you realize there are greater forces at play than previously considered.
When this whole story happened, Yitzchak realized it was from heaven and that there must have been reasons why Yaakov was more worthy of the brachos than Esav. There must have been reason why it had to happen and turn out the way it did. He was probably even relieved that he had been saved form making a horrible mistake.
Ytzchak did not need to criticize Yaakov or even ask for an explanation. he now realized that there were greater forces at play.