Tom, I have to disagree with almost everything you're saying.

I'm sorry, but nothing you've said about Dumbledore has me convinced, and perhaps it's because you use unsupported conjectures more than anything else. I have no problem with making conjectures when evidence is lacking, because we don't have all the evidence yet, but they have to be supported by something else too, especially if they are to contend with supported arguments. If you cite literary techniques, show us examples of where they've been used, so that their true merit can be examined.
To put it bluntly, you're using conjectures based on literary themes, but you're not citing any examples, so at this stage, it's your opinion against some reasonably substantial evidence. Like Anglar said, all we know about the Unbreakable Vow is that it is, supposedly, unbreakable. Pedantically, yes, we can't be certain, but as far as probability goes, you haven't really got anything to go on.
When I say evidence, I don't necessarily mean hard evidence. Something from the books, supported by an example in literature that aids in interpreting it in a certain way is enough, but you haven't given us that. I'm specifically talking about the mentor figure who didn't die. I know you're thinking of Gandalf (I know what JK Rowling said, and I know you know!

) as an example of it being done in literature, but Tolkien is the only author I know of who brought the mentor back, and only in such a way that he couldn't be of any help to the hero in the final stage, which means that he too conformed to the traditional role of this archetype. If there aren't any examples of a mentor coming back to help the hero, JK Rowling must be the first author in the history of known (and quality) literature over thousands of years to do that, and you must admit, the odds against that are huge. Odds so big, in fact, that in this day and age of reason and logic, no one would consider that a chance at all.
Why, speaking in terms of literary devices, would Albus Dumbledore have to return? So everyone can take hands for the curtain call, like in a comedy? Sorry, Tom, that's too weak. The only thing
required for something to qualify as a comedy is a happy ending, and since the ending is the one thing we
don't know, you can hardly cite that as a reason.
The humorous style isn't evidence for a comedy, because there are humorous passages in Macbeth too. In essence, a comedy is a story of the rise in fortune of a sympathetic central character, directly opposed to tragedy, which is about the deterioration of a great character. I see very little of the comic hero in Harry Potter. He's not rising in fortune at all. The story could rather be a tragedy -
definitely worth a look.
On the squib topic, just because it's fun, if a squib is someone who can't do magic, and a there is someone who will do magic later on, they wouldn't be a squib, but rather, they would be wrongfully thought of as a squib. Or wrongfully thought of as a muggle, in Aunt Petunia's case. It's not a squib doing magic, it's someone
thought to be a squib doing magic. But ok, yep, that's off topic.
Can I just ask (sorry, the logic of the argument escaped me over several pages), what does it prove if Snape had managed to break the Unbreakable Vow? That he killed Aberforth instead of Albus, because Voldemort specifically meant Albus?
Hmm, forgive me, but Snape breaking the Unbreakable Vow is merely a secondary plot device then, so why invent an Unbreakable Vow in the penultimate book, which isn't really unbreakable, just to pass a plot point that is secondary anyway. Why raise the stakes so high by making death the punishment, just to let it fizzle out in a feeble sort of way when we find out it wasn't so dire after all? It's a little far-fetched, and has to contend with the simple and weightily supported idea that Albus Dumbledore really did die, and in so doing, stepped out of the final stretch for the hero, like many mentor figures before him. That
is supported in literature.
Can you see the odds tottering precariously to one side?