The military demarche on the hospital logically was ordered by Batista. Perhaps Johnny Ola's body was found, and Batista or someone in SIM (his "gestapo") figured Roth would be next. Or, Batista knew he was going to resign, and as a last favor to his "old friend and associate from Florida," ordered his loyalists to take Roth out of the hospital and put him on a boat--and just happened on the bodyguard doing his dirty deed. But, I like to let my imagination ramble by connecting Fredo's getting "a real drink" with what was shown in the very next scene.