Yu is clearly the Wild Card still having been summoned to the velvet room again, had the opportunity presented itself and he actually killed some shadows I bet he coulda began fusing again.
Aigis however is iffy her "The Fool" Wild Card power in The Answer was never really her's to begin with, the P3 MC gave it to her along with his persona and at the end of The Answer she promised to live her own life (The end theme Brand New Days explaining a lot of that.) which could be her taking up the mantle of "The Fool" herself with her own personas... Which might be why she is still labeled "The Fool" in Arena but uses her two Chariot arcana personas.
Why wouldn't they? I thought the power of the Wild Card was something people are born with, and not some temporary things granted by the Velvet Room. Sure the Velvet Room unlocks the full potential, but they still have the Wild Card regardless. Unless I'm wrong, in which case I'd appreciate being told so. I know Aigis' case is different, but I thought that was because P3's MC gave her his power.
Blades will bleed. Shields will shatter. But as the light fades, will The Hero rise again? Or will Darkness reign? ~ Zelda TP Trailer 1