Yes, it would.
>Anger Point raises the ability-bearer's Attack to its maximum level - +6 stages or 4× usual power - when a move targeting it receives a critical hit.
So yes it would, because the ability has activated and already raised the Attack to +6. Just because the ability changes won't remove the +6.
It's like you have a Weakness Policy. It activates, and you get your +2 Attack and Sp. Attack. If it was Knocked Off, or removed before the end of battle in any other way, would you lose the +2? (Or +4, if you're counting both) No, of course not.
If you had Swords Dance, and you used it, and you get your +2 Attack. If it was disabled, would you lose the +2 bonus? No.
You would keep your +6
Description of Anger Point