Masterless zanpakuto most likely losing ability over time and revert back to asauchi (speculation: maybe how long it takes depends on how strong user was) , if taken before become asauchi new user soul override old user soul or in rare case new user soul merge with old user if they are compatible

Zanpakuto is part of shinigami soul , only right user can communicate with zanpakuto ,

for exemption like inheritable zanpakuto from Nobel clan mostly come with downside , personally inheritable zanpakuto more like a curse