Rejoining the two could be a land mine: CBS would risk angering shareholders if it offered too much of a premium for the lagging Viacom, while the latter’s investors would be upset if they did not get much more than its market value.

There is another wrinkle, too: Industry merger activity has gone on a tear since the Redstones made their CBS-Viacom pitch in September. AT&T’s surprise $85 billion October offer for Time Warner came with a rich 36 percent premium. And on Friday, 21st Century Fox suggested paying two-fifths more than the current share price for the 61 percent of the European pay-TV operator Sky that it does not already own.

Now free to pursue their separate paths, the Redstones’ two companies will probably look for other ways to scale up. CBS could attract rivals hoping to replicate AT&T’s plan of combining content with distribution. Verizon, the $209 billion telecom giant, would be one contender. Viacom may fit with other cable networks, including those currently being assembled by Liberty Media’s John Malone.