For all of his paranoia concerning the prophecy and the scabbards and Kozuki family Orochi was really unable of suspecting his own followers and allies, whenever it was Kyoshiro or Komurasaki or his benefactor Kaido.
Orochi should have known that it's always very dangerous to be entirely reliant on and to owe everything to one man like Kaido and that he was never Kaido's equal.
Even Doflamingo who views himself as godly knew that he was not Kaido's equal.
However I don't think that Orochi nor that Kanjuro are dead. Weeds are hard to kill after all and Orochi has a df that may protect him from even decapitation given that the Orochi snake has 8 heads and can endure an absurd lot of punishement like its western cousin the Hydra of Lern. Plus it's possible that Oda could have given the Hydra's ability to the Orochi zoan.
Also Kanjuro is a master actor and painter and he certainely hasn't show the full extent of the tricks he can do with his df.