Board Thread:Warhammer 40k General Discussion/@comment-108.51.155.155-20131208175717/@comment-6078851-20140428122353

luther didn't triumph over the lion: el'jonson was on the verge of killing luther and had technically won but couldn't bring himself to slay his surrogate father, his brother, his friend, whereupon luther took advantage of jonson's hesitation, effectively blind-siding him, but jonson was way more than capable of killing luther.

the emps vs horus fight was similar - horus could have been seen as holding his own against emps, or maybe even gaining the advantage, but the truth was that horus was entirely outclassed and emps only ended the fight once he realised that horus was beyond redemption. the jonson vs luther fight could show that jonson had more compassion than emps (or maybe he just didn't see how far luther had fallen) as he couldn't bring himself to kill his oldest friend, but luther was still outclassed.

i think probably any primarch would be able to permanently kill abbadon. i doubt any of ork-kind could although tyranids with the hive mind and the suffocating shadow in the warp may be able to.