Raw, that’s a hell no because the NPC didn’t agree to be turned into a sword (and iirc, that’s outside the scope of the spell anyway, no inanimate objects).
It’s really not something that would work in a stable game setting.
That being said, it could still be allowed without being game breaking as long as the DM is willing to make the exception to the rules have a reason for happening. Say, the NPC had gained the attention of some entity that took the opportunity to intervene. Or maybe the NPC felt it coming, and decided to go along with it for nefarious purposes. There’s all kinds of single event exceptions possible.
True Polymorph can turn people into objects.
Eh, back in 2e Polymorph worked a lot like True Polymorph does in 5e, in 3e it was called Polymorph Any Object. I think a lot of players just call it Polymorph, even though there’s a level four spell with the same name, especially if the context of the situation makes it clear which spell is being used. At least that’s how it goes at my table, but every group is different.
