Yeah I don't want any of Zoro's swords to break either but it's hard to think of a power up for Zoro now.
We know that turning a black blade is a given for Zoro
But what's gonna be the impetus for it? Zoro is just not gonna make a black blade on the fly without sacrificing anything.
So, the most obvious answer, is Sandai has to break. We're already introducted to its higher-quality replacement for it.
Poor Sandai
I hope King at least stepped on it after disarming Zoro.