What does Kendall do next?
A better question might be: Is Kendall healed? Over the course of the second season, Kendall slowly started to regain his terrier-like instincts, culminating in his aggressive defense of his dad during the congressional testimony in the penultiamte episode, "DC." But in blowing up his life, there's no clear path going forward. He could side once again with Stewy and Sandy Furness, whose bear-hug takeover of Waystar still looms. But would those two accept Kendall, who previously betrayed them for his father, back into their ranks? On the other hand, he could be hyper-aware that he's digging his own grave, and dragging his dad into it with him. Regardless, he's drawn a very clear line for the rest of his family to start strategically choosing sides.
What does this mean for Logan?
Logan has a clear move if he wants to fully annihilate Kendall: He can tell the world how his son was responsible for a young man's death. But, aside from that nugget of titillating and tragic information, it's unclear what other cards Logan has to play. And while invoking the killing would certainly take his son down, it wouldn't absolve the elder Roy of the misdeeds detailed in Greg's documents. Prison time isn't a given; the rich and powerful have long circumvented the U.S.'s criminal justice system.
Then there's that inscrutable look on his face in the season's final shot. He looks almost pleased that Kendall decided to fight back, but if he truly wants to keep the company in his control, he's going to have to work some Machiavellian magic. Or, per speculation humming around Twitter, maybe Logan has been pulling the puppet strings all along. But as Brian Cox told Vulture, "The smile is him saying, 'Finally, my son is stepping up to the plate, doing what he needs to do to run a business. Finally, he's the heir apparent to Waystar Royco.' In a way, it's a completion. But there's life in the old dog yet! We've got quite a journey now. Logan has to reclaim himself. He needs to even the odds."