Green’s Dictionary of Slang

killed off adj.

dragged out from one’s recumbent position beneath a table after drinking to excess.

[UK]‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 109: Killed off — those of a large party who may have taken quantum suff. to send them away from the table.
[UK]H. Baumann Londinismen (2nd edn).