Did Hijikata and Kondo kill Oboro?
The fight you mention happens in episode 315. Hijikata slashes at Oboro's lower right abdomen and Kondo cuts at his left arm, and we see Oboro fall down. These are not necessarily fatal wounds, plus if you add the fact the Oboro has some of Utsuro's immortal blood inside him, it's actually probable that Oboro survived after that fight. He only dies later on in his final fight with Takasugi.