though it is always a possibility
Yeah, and we shouldn't dismiss that possibility until it's confirmed or denied.
It's alright. You won't need to apologize in the future. I'm just saying that Vergil keeping his moves will most likely happen.
He was surprised before the final run.
No, he was surprised both before and after the final run. He was shocked that his last gambit didn't pay off. You can see it with his wide-open eyes and gaping mouth expression.
He was shocked that the final run didn't work.
First off, he didn't decide to "join the demons". Heck, he goes against Mundus the Demon King right after the fall! And that's another act of pride and over-confidence, btw ("If my father did it, I should be able to do it too.").
Second, the pride resides in the fact that rather than accepting Dante's help to return to the human world, he preferred to remain trapped in the Netherworld where his father lived before him. Simple as that.
But he was working with the Hell Vanguard in the beginning. When the Vanguard came back he punished it for its failure to put up a decent fight against Dante.
Besides, the Hell Vanguard didn't attack Vergil. It was just standing there, as if awaiting orders.
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Sure, he fought against the demons guarding the tower in the beginning, but who's to say that he had to fight them afterwards? Besides Beowulf, it looked like he was in league with the evil demons themselves.
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The fact that he decided to fight against Mundus was just him wanting more power. That's it.
Besides, overconfidence does NOT mean true pride. It just means you're foolish.
Like his fight with Dante, Vergil thought he could actually win against Mundus because like you said, Vergil stated:
"If my father could do it, I should be able to do it too."
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When he runs towards Mundus screaming, we don't see what happens after that. We never know if Mundus offered him a deal, or if he just memory-wiped Vergil with a wave of his hand.
We don't know how Mundus dealt with Vergil after Vergil was foolish enough to think he could win against Mundus.
If Vergil didn't have the pride to be defeated by Dante, then he
almost certainly wouldn't have had the pride to be defeated by Mundus.
Mundus most likely wiped Vergil's memory before Vergil could even get close to him.
Or, perhaps Mundus offered Vergil power (because Vergil was more powerful as permanent DT Nero Angelo) and wiped his memory after that.
Or maybe the power that Mundus offered corroded Vergil's mind on its own and wiped his memory that way. That's probably what most likely happened.
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Vergil didn't want to return to the human world because there really isn't any power there. He could only find it in the demon world. It has nothing to do with "True Pride."
Vergil knows that Sparda would be ashamed of the fact that his son would stay in a world he tried to hard to escape.
The Dark Son of Sparda knows this but doesn't care. Vergil went into the demon world and challenged Mundus because he thought he could actually defeat Mundus.
Vergil probably thought that Dante "just got lucky" and he still thinks he's the "stronger son of Sparda."
He really did think he could defeat Mundus because he thought that he was just as powerful as Sparda was.
This is Vergil being foolish, shameful, and cowardly up until the very end, when Mundus stopped him -- either by offering Vergil power or just plain wiping his memory before Vergil could even get close to him.
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So... I still think that Vergil isn't proud. He thought Mundus was an easy target because in his mind, he's just as powerful as Sparda. Losing to Dante never changed that.
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Personally, I think if it ever occured to Vergil during his final battle with Mundus that he would lose, he would most likely just run away again like he did with Dante.
