If a champion dies... a message goes out in the chat box that mentions the champion being killed by... whatever killed them, much like how a message appears when a player/tamed mob dies. Example...

'mob Champion' was slain by 'player'.

'mob Champion' suffocated in a wall

'mob Champion' was killed by wild bees. They should've used a Smoker.

'mob Champion' walked into a cactus whilst trying to escape 'player'

etc. etc. etc.

Could be a config option enable/disable the message.