Nothing happens as Totsuka only seal the living ones, it has never sealed inanimate object or jutsu so TSB passes through it or next to it then meet Yata Mirror.
That when it become really debate
Naruto-wiki, it states that totsuka blade seals anything it pierces.
But the thing about the Truth-Seeking Ball is that it (and I quote these) "can be shaped into a variety of forms, allowing them the flexibility to be used for offensive, defensive, and supplementary purposes." - "this technique can utilise Yin–Yang Release to nullify all ninjutsu the balls touch." -
I'm not sure how TSB will do, but it makes sense for it to turn Totsuka blade to dust, seeing that it's a weapon.