When a Slayer is reduced to zero wounds, he makes a single Deathblow attack against an enemy model that is in base contact with him.
That's not the rule.
Any enemy model in base contact. Not "an enemy model in base contact with him". You're rewriting the book to suit your argument.
The 'him' is heavily implied in the context. You can read into it and extract 'in base contact with the Slayer unit', but I find it unlikely that is the intended interpretation.
if more than one model is in base contact with him, he gets to choose which model to attack with his Deathblow. The only thing that makes a Deathblow attack different than a regular attack is that it is performed out of sequence when the Slayer is killed, so all the "normal" rules for attacking are followed, with the exception of striking order.
This is also not the rule as written in the army book.
You're really helping me make my case.
Here's the riddle for you - a lord on a 20mm base is in a unit of four total models, including himself. His unit is in base contact with a unit of 20 models, deployed in two ranks.
The Lord is in base contact with only three models, but he's got three stacks of Fury. He hits 12 times, and wounds twelve times. By the logic you're using regarding Deathblow, this lord can only kill six models, since they are the on,y models that can be considered to be in contact with him. Obviously, that's not how things work.
As you say, this is a abstraction. So, too, is deathblow.
I agree, there's a level of abstraction in both cases...
Which specific models move up doesn't really matter in most cases: the models behind move forward and sideways to fill the gaps. It's an abstraction of the press of combat, and it does a pretty good job of representing what the reality would be. Supporting attacks are made over or through the front rank, and every model that was hit is assumed to be in base contact at the moment they're hit.
You cannot have it both ways. Deathblow is also an abstraction of the press of combat.
The BRB section on Close Combat states that "Normally, a model can only strike blows against an enemy model in base contact. The most common exception is when he is making a supporting attack.
Again, by your logic, a model can only kill as many models as are in contact with it in the first rank. After that, models are no longer actually in base contact, and cannot be struck, right?
Meh, both are abstractions, but reading it as 'the unit' in contact allows and implies far more levels of 'abstraction' like allowing a slayer killed by a unit in its front to kill a model in the rear of the unit. If instead, you read it as 'in base contact with the model', but you 'abstract' that to allow him to strike any model that he could have 'feasibly' been in base contact with, you're getting closer. The Slayer 'steps up' per the description of removing models, and is then in base contact (even though our abstraction doesn't have us move the model that way), gets killed, and then directs his attack at a model in the attacking unit that is in the first rank.
So I repeat: GW uses the same phrase ("base contact") to mean both "base contact with the unit" OR "base contact with the specific model." They use the terms freely and interchangeably. Since the entirety of the Deathblow special rule is referring to the individual model (reduced to zero wounds, number of attacks on his profile, etc) and does not mention his unit, it's probable that "in base contact" is ALSO referring to the individual model, rather than his unit.
So, explain the sword of anti heroes.
But I don't see how "base contact" can possibly always mean what you're claiming it always means.
Base contact, in this context, means exactly what I've argued, because the slayer can target *any* model in base contact! and we don't know where the dead slayer actually came from! since as you say hits and wounds are an abstraction.