Not exactly, Roxas always has two Keyblades in the DDD opening, even in the Keyblade Graveyard-scenes:
If you look closely, you'll see the white "pummel" of the end of the handle from the Oathkeeper at the bottom right of this pic, directly left of Roxas' left arm.
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As for him still dual-wielding, well, when he becomes an individual on his own terms (although still connected to Sora, he isn't treated like a cheap replacement-copy anymore) giving him the dual-wielding would make him a bit more unique, IF they would decide to finally leave the dual-wielding to him alone.
As for how that might work, tsk, since when has it been above Nomura to introduce "exceptions to rules" when "rule of cool" demands it.
He could very easily claim that since Roxas' new heart was made from both Sora's and Ven's hearts it has grown with two wielding abilities, allowing him to wield two Keyblades at all times.