It'll be bad PR if they don't honor it, though. Purchasers of the NFT don't know the original holder got banned, and they have every reason to assume buying the NFT from that person will give them whatever privilege or cosmetic it's supposed to grant them in-game. Enough people don't have that happen and complain about it loudly enough and Ubisoft will feel pressure to change their policies to honor it.
It'd be a stupid hill to die on anyway. Granted Ubisoft has done some stupid stuff in the past, but this one I don't think they'd win in the end.
And according to the article they got pushback, said it was a glitch (his got deleted after a year of inactivity, they claim it's supposed to be four years, and in part to comply with data privacy laws, I'm guessing in the UK as theirs are pretty stringent), and also said they're going to more or less undo it in this instance, meanwhile Steam wasted no time announcing they don't delete inactive accounts ever, gaining some free brownie points and a decent number of people will probably avoid their store in the future so as not to risk this happening.
So yeah, I maintain my point that if they offer NFTs, allow owners to sell them to other people (which is kind of the point of NFTs), and then decide certain instances of NFTs don't have to be honored because they banned that person, they're going to get enough articles like this that they'll feel pressure to walk back such an action.
It'd be a stupid hill to die on anyway. Granted Ubisoft has done some stupid stuff in the past, but this one I don't think they'd win in the end.