The following contains SPOILERS.
Terry Silver returned in Cobra Kai season 3, albeit in flashbacks. We see how Sensei Kreese heroically saved his ass in Vietnam, leading to Silver to vow; ‘… anything you need, I’m there for you, your whole life. Your whole life’.
At the end of season 3 we see turncoat Johnny Lawrence team up with sleazy car salesman Daniel LaRusso to double team a man in his senior years, after also stealing his students. Naturally he calls for some backup.
Kreese is clearly on the phone to Sensei Silver.
Now, producer Jon Hurwitz all but confirms the return of Thomas Ian Griffith in season 4. Speaking to Entertainment Weekly he says:
At the end of the season, you saw Kreese make a phone call. You could guess who might’ve been on the other end of that call based off of the photo that he was looking at there.
“But we can’t really speak to how Terry Silver would respond to that call.
Hurwitz also acknowledged the popularity of Sensei Silver: ‘We know how beloved the character Terry is’. And with that, what is sure to be the greatest moment in television history will occur in the fourth season of Cobra Kai.