Ah but that Slayer is Gotrek Gurnisson, the mightiest living Slayer (and also possibly the unluckiest as he still hasn’t met his glorious death) except for perhaps Ungrim Ironfist himself. Throgg may have been one of the most broken characters in 8th Edition but Gotrek would have counted as both a Dragon and a Daemon Slayer if he had had an 8th Ed profile, so his wounds would have had the multiple wounds(D3) special rule, have always wounded on 4s or above and would have forced Throgg to re-roll successful Ward Saves if he had any. I don’t know if Chaos Trolls have Regeneration like ordinary Trolls do but that would probably be the only thing that could save him from Gotrek, and every wound that he fails to regenerate would be multiplied into D3 wounds so he would be in trouble I believe.
Lore-wise he would be Throgg.... but not Archaon. Gotrek in the novels is an unstoppable killing machine. Throgg does have Regeneration and has 4 wounds. This would be a very simple fight... either Gotrek kills him first round (because Throgg has ASL) or Throgg kills him immediately afterwards. Gotrek, with no defense, has no chance to withstand Throgg's counter attack. It is literally a case of kill or be killed. It could go either way.