Board Thread:Questions and Answers/@comment-24769684-20151201164320/@comment-11051098-20151201202725

Mayuri stated once that he can remodel his Zanpakuto to something similar to what it was if it breaks. I believe that was going for both Shikai and Bankai, though I'm not 100 % sure.

Either way, he has modified his Bankai so much over time that I doubt it's a far stretch to believe that he could remodel even a broken Bankai.