Board Thread:General Discussion/@comment-3244769-20140121195139/@comment-6007020-20140121203713

Zanpakuto cannot be restored if their Bankai form is destroyed, not broken, and I don't remember Szayelaporro destroying Hihiō Zabimaru, unless I missed something. Also, Mayuri mentions that his Bankai was destroyed once and he didn't restore it, only remodeled it. Perhaps he did the same for other Shinigami whose Zanpakuto are permanently damaged?

Also, Tosen's Zanpakuto also exists in sword form while the area of blindness is active, so you'd want to target the blade, though I don't see that as being easy.